diff --git a/website/src/lib/components/collapsible-tree/CollapsibleTreeNode.svelte b/website/src/lib/components/collapsible-tree/CollapsibleTreeNode.svelte
index a9d33139c..e24caffb9 100644
--- a/website/src/lib/components/collapsible-tree/CollapsibleTreeNode.svelte
+++ b/website/src/lib/components/collapsible-tree/CollapsibleTreeNode.svelte
@@ -10,7 +10,8 @@
         id: string | number;
         class?: ClassValue;
         trigger: Snippet;
-        content: Snippet;
+        /** Gets whether the node is open, for contents that are only worth building then. */
+        content: Snippet<[boolean]>;
     } = $props();
 
     let state = getContext<CollapsibleTreeState>('collapsible-tree-state');
@@ -88,6 +89,6 @@
         </Button>
     {/if}
     <Collapsible.Content>
-        {@render props.content()}
+        {@render props.content(open.current)}
     </Collapsible.Content>
 </Collapsible.Root>
diff --git a/website/src/lib/components/explorer/Explorer.svelte b/website/src/lib/components/explorer/Explorer.svelte
new file mode 100644
index 000000000..a82f4713f
--- /dev/null
+++ b/website/src/lib/components/explorer/Explorer.svelte
@@ -0,0 +1,50 @@
+<script lang="ts">
+    import { CollapsibleTree, CollapsibleTreeNode } from '$lib/components/collapsible-tree/index';
+    import { ScrollArea } from '$lib/components/ui/scroll-area/index';
+    import ExplorerTree from './ExplorerTree.svelte';
+    import { i18n } from '$lib/i18n/i18n.svelte';
+    import { engine } from '$lib/engine';
+    import { folderName } from '$lib/engine/workspace';
+
+    const { workspace } = engine;
+
+    let folder = $derived($workspace?.folder);
+</script>
+
+<!--
+    The tree of the open folder: its folders and GPX files, one level read at a time. The files are
+    opened from it (the file list has the ones that are open).
+-->
+{#if folder}
+    <div class="flex flex-col h-full">
+        <div class="px-2 py-1 text-sm font-semibold shrink-0">{i18n._('menu.explorer')}</div>
+        <ScrollArea class="grow min-h-0">
+            <div class="flex flex-col pl-1 pr-3 pb-1">
+                <!-- starts over when another folder is opened -->
+                {#key folder}
+                    <!-- the folder itself, which is open at first -->
+                    <CollapsibleTree side="left" defaultState="open">
+                        <CollapsibleTreeNode id="folder">
+                            {#snippet trigger()}
+                                <span class="grow truncate text-left" title={folder}>
+                                    {folderName(folder)}
+                                </span>
+                            {/snippet}
+                            {#snippet content(opened)}
+                                <!-- what is in it is only read when it is open -->
+                                {#if opened}
+                                    <div class="ml-4">
+                                        <!-- its folders are closed at first -->
+                                        <CollapsibleTree side="left" defaultState="closed">
+                                            <ExplorerTree />
+                                        </CollapsibleTree>
+                                    </div>
+                                {/if}
+                            {/snippet}
+                        </CollapsibleTreeNode>
+                    </CollapsibleTree>
+                {/key}
+            </div>
+        </ScrollArea>
+    </div>
+{/if}
diff --git a/website/src/lib/components/explorer/ExplorerTree.svelte b/website/src/lib/components/explorer/ExplorerTree.svelte
new file mode 100644
index 000000000..cf2f770d0
--- /dev/null
+++ b/website/src/lib/components/explorer/ExplorerTree.svelte
@@ -0,0 +1,80 @@
+<script lang="ts">
+    import { CollapsibleTreeNode } from '$lib/components/collapsible-tree/index';
+    import { Button } from '$lib/components/ui/button';
+    import { FileText } from '@lucide/svelte';
+    import ExplorerTree from './ExplorerTree.svelte';
+    import { openPath } from '$lib/actions/file-actions';
+    import { engine, type FolderEntry } from '$lib/engine';
+    import { selectedFileIds } from '$lib/engine/selection-helpers';
+    import { fileIdAt } from '$lib/engine/workspace';
+
+    let {
+        path,
+    }: {
+        /** The folder whose content is listed, the open folder if it is not given. */
+        path?: string;
+    } = $props();
+
+    const { workspace, selection, folderVersion } = engine;
+
+    let entries: FolderEntry[] = $state([]);
+
+    $effect(() => {
+        // read again when something changed on the file system
+        $folderVersion;
+        let current = true;
+        engine.listFolder(path).then((list) => {
+            if (current) {
+                entries = list;
+            }
+        });
+        return () => {
+            current = false;
+        };
+    });
+
+    /** Opens the file, or selects it if it is open already. */
+    function open(entry: FolderEntry, id: string | undefined) {
+        if (id !== undefined) {
+            engine.select([id]);
+        } else {
+            openPath(entry.path);
+        }
+    }
+</script>
+
+{#each entries as entry (entry.path)}
+    {#if entry.isDir}
+        <CollapsibleTreeNode id={entry.name}>
+            {#snippet trigger()}
+                <span class="grow truncate text-left">{entry.name}</span>
+            {/snippet}
+            {#snippet content(opened)}
+                <!-- the content of a folder is only read when it is opened -->
+                {#if opened}
+                    <div class="ml-4">
+                        <ExplorerTree path={entry.path} />
+                    </div>
+                {/if}
+            {/snippet}
+        </CollapsibleTreeNode>
+    {:else}
+        {@const id = fileIdAt($workspace, entry.path)}
+        {@const selected = id !== undefined && selectedFileIds($selection).includes(id)}
+        {@const dirty = id !== undefined && $workspace?.files[id]?.dirty === true}
+        <Button
+            variant="ghost"
+            class="w-full h-7 px-1 justify-start gap-1.5 border-none font-normal {selected
+                ? 'bg-accent'
+                : ''} {id === undefined ? 'text-muted-foreground' : ''}"
+            title={entry.path}
+            onclick={() => open(entry, id)}
+        >
+            <FileText size="16" class="shrink-0" />
+            <span class="grow truncate text-left">{entry.name}</span>
+            {#if dirty}
+                <span class="size-1.5 shrink-0 rounded-full bg-foreground"></span>
+            {/if}
+        </Button>
+    {/if}
+{/each}
diff --git a/website/src/lib/components/explorer/index.ts b/website/src/lib/components/explorer/index.ts
new file mode 100644
index 000000000..6b86bed1c
--- /dev/null
+++ b/website/src/lib/components/explorer/index.ts
@@ -0,0 +1 @@
+export { default as Explorer } from './Explorer.svelte';
diff --git a/website/src/lib/components/file-list/FileList.svelte b/website/src/lib/components/file-list/FileList.svelte
index 96a6dd2d6..d3c1b523c 100644
--- a/website/src/lib/components/file-list/FileList.svelte
+++ b/website/src/lib/components/file-list/FileList.svelte
@@ -36,14 +36,14 @@
 </script>
 
 <ScrollArea
-    class="shrink-0 {orientation === 'vertical' ? 'p-0 pr-3' : 'h-10 px-1'}"
+    class="shrink-0 {orientation === 'vertical' ? 'p-0' : 'h-10 px-1'}"
     {orientation}
     scrollbarXClasses={orientation === 'vertical' ? '' : 'hidden'}
     scrollbarYClasses={orientation === 'vertical' ? '' : ''}
 >
     <div
         class="flex {orientation === 'vertical'
-            ? 'flex-col py-1 pl-1 min-h-screen'
+            ? 'flex-col py-1 pl-1 pr-2 min-h-screen'
             : 'flex-row'} {className ?? ''}"
         {style}
     >
diff --git a/website/src/lib/components/file-list/sortable-file-list.ts b/website/src/lib/components/file-list/sortable-file-list.ts
index 764d9a042..7f4cfb341 100644
--- a/website/src/lib/components/file-list/sortable-file-list.ts
+++ b/website/src/lib/components/file-list/sortable-file-list.ts
@@ -32,6 +32,14 @@ export class SortableFileList {
     private _sortable: Sortable | null = null;
     private _elements: { [id: string]: HTMLElement } = {};
     private _updatingSelection: boolean = false;
+    /**
+     * Whether a change of the selection that this list made is being applied by the engine. A click
+     * makes several events, handled after one another, and the engine can answer after them (in
+     * the desktop app, it is in another process): until it has, the list holds the selection, and
+     * the engine and the list disagree because the engine is behind, not because the user did
+     * something else.
+     */
+    private _applying: boolean = false;
     /** The elements of the list when a drag from it started, to put them back when it ends. */
     private _snapshot: ChildNode[] = [];
     private _unsubscribes: (() => void)[] = [];
@@ -196,6 +204,9 @@ export class SortableFileList {
     }
 
     updateFromSelection() {
+        if (this._applying) {
+            return;
+        }
         const changed = this.getChangedIds();
         if (changed.length === 0) {
             return;
@@ -220,7 +231,7 @@ export class SortableFileList {
 
     updateToSelection(e: Sortable.SortableEvent) {
         if (!this._sortable) return;
-        if (this._updatingSelection) return;
+        if (this._updatingSelection || this._applying) return;
         this._updatingSelection = true;
         const changed = this.getChangedIds();
         if (changed.length == 0) {
@@ -242,28 +253,41 @@ export class SortableFileList {
         }
 
         const parent = this._parent;
+        let request: Promise<boolean>;
         if (selected.length === 0 || !this.childNode(selected[0])) {
-            engine.select([]);
+            request = engine.select([]);
         } else {
             switch (this._sortableLevel) {
                 case 'file':
-                    engine.select(selected);
+                    request = engine.select(selected);
                     break;
                 case 'track':
-                    engine.selectTracks(parent!.fileId, selected);
+                    request = engine.selectTracks(parent!.fileId, selected);
                     break;
                 case 'segment':
-                    engine.selectSegments(parent!.fileId, (parent as any).trackId, selected);
+                    request = engine.selectSegments(
+                        parent!.fileId,
+                        (parent as any).trackId,
+                        selected
+                    );
                     break;
                 case 'waypoints':
-                    engine.selectWaypointGroup(parent!.fileId);
+                    request = engine.selectWaypointGroup(parent!.fileId);
                     break;
                 case 'waypoint':
-                    engine.selectWaypoints(parent!.fileId, selected);
+                    request = engine.selectWaypoints(parent!.fileId, selected);
                     break;
             }
         }
         this._updatingSelection = false;
+
+        // the events of the same click that come before the engine answers are not new choices
+        this._applying = true;
+        request.finally(() => {
+            this._applying = false;
+            // the list shows what the engine selected
+            this.updateFromSelection();
+        });
     }
 
     updateFromFileOrder() {
diff --git a/website/src/lib/engine/backend/tauri.ts b/website/src/lib/engine/backend/tauri.ts
index 004862191..1bc677e1f 100644
--- a/website/src/lib/engine/backend/tauri.ts
+++ b/website/src/lib/engine/backend/tauri.ts
@@ -221,12 +221,13 @@ export async function createTauriBackend(): Promise<Backend> {
             exportFiles: (fileIds, options) =>
                 invoke<boolean>('export_files', { fileIds, options }),
             listFolder: (path) => invoke<FolderEntry[]>('list_folder', { path }),
-            listen: async (onEngineChanged, onWorkspaceChanged, onFilesOpened) => {
+            listen: async (onEngineChanged, onWorkspaceChanged, onFilesOpened, onFolderChanged) => {
                 await listen<Outcome>('files-opened', (event) => onFilesOpened(event.payload));
                 await listen<Outcome>('engine-changed', (event) => onEngineChanged(event.payload));
                 await listen<WorkspaceState>('workspace-changed', (event) =>
                     onWorkspaceChanged(event.payload)
                 );
+                await listen<string[]>('folder-changed', () => onFolderChanged());
             },
         },
 
diff --git a/website/src/lib/engine/backend/types.ts b/website/src/lib/engine/backend/types.ts
index 5ba870fa6..6cb1548c1 100644
--- a/website/src/lib/engine/backend/types.ts
+++ b/website/src/lib/engine/backend/types.ts
@@ -91,13 +91,15 @@ export interface DesktopFiles {
     listFolder(path?: string): Promise<FolderEntry[]>;
     /**
      * Tells when the engine changed without being asked, because the files on the disk did (the
-     * outcome to apply), when the status of the files changed, and when files were opened with the
-     * app from the system (the outcome to apply, which selected them).
+     * outcome to apply), when the status of the files changed, when files were opened with the
+     * app from the system (the outcome to apply, which selected them), and when something changed
+     * in the open folder (the tree of its files is to be read again).
      */
     listen(
         onEngineChanged: (outcome: Outcome) => void,
         onWorkspaceChanged: (workspace: WorkspaceState) => void,
-        onFilesOpened: (outcome: Outcome) => void
+        onFilesOpened: (outcome: Outcome) => void,
+        onFolderChanged: () => void
     ): Promise<void>;
 }
 
diff --git a/website/src/lib/engine/engine.ts b/website/src/lib/engine/engine.ts
index cac566810..b54344643 100644
--- a/website/src/lib/engine/engine.ts
+++ b/website/src/lib/engine/engine.ts
@@ -65,6 +65,7 @@ class Engine {
     private _lastError = writable<string | undefined>(undefined);
     private _outdated = writable(false);
     private _workspace = writable<WorkspaceState | undefined>(undefined);
+    private _folderVersion = writable(0);
     private _canUndo = writable(false);
     private _canRedo = writable(false);
     private _canPaste = writable(false);
@@ -86,6 +87,11 @@ class Engine {
     readonly workspace: Readable<WorkspaceState | undefined> = {
         subscribe: this._workspace.subscribe,
     };
+    /**
+     * A number that changes when something changed in the open folder on the file system, to read
+     * its tree again.
+     */
+    readonly folderVersion: Readable<number> = { subscribe: this._folderVersion.subscribe };
     /** Why the last call to the engine did nothing, `undefined` if it did something. */
     readonly lastError: Readable<string | undefined> = { subscribe: this._lastError.subscribe };
     /** What was copied or cut, waiting to be pasted. */
@@ -689,7 +695,8 @@ class Engine {
                     await this.sync(backend, outcome);
                     this.report(outcome);
                     this._opened.forEach((callback) => callback(outcome.added));
-                })
+                }),
+            () => this._folderVersion.update((version) => version + 1)
         );
     }
 
diff --git a/website/src/lib/engine/workspace.test.ts b/website/src/lib/engine/workspace.test.ts
index 0854b30df..8579e5286 100644
--- a/website/src/lib/engine/workspace.test.ts
+++ b/website/src/lib/engine/workspace.test.ts
@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
-import { folderName, subfolder } from '$lib/engine/workspace';
+import { fileIdAt, folderName, subfolder } from '$lib/engine/workspace';
 
 describe('subfolder', () => {
     it('is where a file is in the folder', () => {
@@ -27,3 +27,23 @@ describe('folderName', () => {
         assert.equal(folderName('C:\\Users\\me\\tracks'), 'tracks');
     });
 });
+
+describe('fileIdAt', () => {
+    const workspace = {
+        files: {
+            a: { path: '/tracks/a.gpx' },
+            b: { path: '/tracks/sub/b.gpx' },
+            c: {},
+        },
+    };
+
+    it('is the open file that is linked to the path', () => {
+        assert.equal(fileIdAt(workspace, '/tracks/a.gpx'), 'a');
+        assert.equal(fileIdAt(workspace, '/tracks/sub/b.gpx'), 'b');
+    });
+
+    it('is nothing for a file that is not open', () => {
+        assert.equal(fileIdAt(workspace, '/tracks/other.gpx'), undefined);
+        assert.equal(fileIdAt(undefined, '/tracks/a.gpx'), undefined);
+    });
+});
diff --git a/website/src/lib/engine/workspace.ts b/website/src/lib/engine/workspace.ts
index 5723c6021..a44ef4ea3 100644
--- a/website/src/lib/engine/workspace.ts
+++ b/website/src/lib/engine/workspace.ts
@@ -26,3 +26,11 @@ export function subfolder(
     }
     return file.slice(root.length, -1).join('/');
 }
+
+/** The id of the open file that is linked to the file at `path`, `undefined` if there is none. */
+export function fileIdAt(
+    workspace: { files: Record<string, { path?: string }> } | undefined,
+    path: string
+): string | undefined {
+    return Object.entries(workspace?.files ?? {}).find(([, file]) => file.path === path)?.[0];
+}
diff --git a/website/src/lib/state/settings.ts b/website/src/lib/state/settings.ts
index 709d5951f..07778f9ea 100644
--- a/website/src/lib/state/settings.ts
+++ b/website/src/lib/state/settings.ts
@@ -156,6 +156,7 @@ export const settings = {
     defaultWidth: new Setting('defaultWidth', browser && window.innerWidth < 600 ? 8 : 5),
     bottomPanelSize: new Setting('bottomPanelSize', 170),
     rightPanelSize: new Setting('rightPanelSize', 240),
+    explorerPanelSize: new Setting('explorerPanelSize', 0),
     /** Takes the saved values (see `Engine.openStorage`). */
     connect(stored: StoredSettings) {
         for (const key in settings) {
diff --git a/website/src/locales/en.json b/website/src/locales/en.json
index 337878a6b..9e88fe6a5 100644
--- a/website/src/locales/en.json
+++ b/website/src/locales/en.json
@@ -14,6 +14,8 @@
         "new_segment": "New segment",
         "open": "Open...",
         "open_folder": "Open folder...",
+        "explorer": "Explorer",
+        "workspace": "Workspace",
         "save": "Save",
         "save_all": "Save all",
         "save_as": "Save as...",
diff --git a/website/src/routes/[[language]]/app/+page.svelte b/website/src/routes/[[language]]/app/+page.svelte
index 063871d12..7a380f79d 100644
--- a/website/src/routes/[[language]]/app/+page.svelte
+++ b/website/src/routes/[[language]]/app/+page.svelte
@@ -2,6 +2,7 @@
     import GPXLayers from '$lib/components/map/gpx-layer/GPXLayers.svelte';
     import ElevationProfile from '$lib/components/elevation-profile/ElevationProfile.svelte';
     import FileList from '$lib/components/file-list/FileList.svelte';
+    import Explorer from '$lib/components/explorer/Explorer.svelte';
     import GPXStatistics from '$lib/components/GPXStatistics.svelte';
     import Map from '$lib/components/map/Map.svelte';
     import Menu from '$lib/components/Menu.svelte';
@@ -23,17 +24,29 @@
     import { getURLForGoogleDriveFile } from '$lib/components/embedding/embedding';
 
     const outdated = engine.outdated;
+    const workspace = engine.workspace;
 
     const {
         treeFileView,
         elevationProfile,
         bottomPanelSize,
         rightPanelSize,
+        explorerPanelSize,
         additionalDatasets,
         elevationFill,
     } = settings;
 
     let bottomPanelWidth: number | undefined = $state();
+    // the file list and the explorer share the right panel, half of it each until it is resized
+    let rightPanelHeight = $state(0);
+    let explorerHeight = $derived(
+        $treeFileView
+            ? Math.min(
+                  Math.max($explorerPanelSize > 0 ? $explorerPanelSize : rightPanelHeight / 2, 60),
+                  Math.max(rightPanelHeight - 80, 60)
+              )
+            : rightPanelHeight
+    );
     let bottomPanelOrientation = $derived(
         bottomPanelWidth && bottomPanelWidth >= 540 && $elevationProfile ? 'horizontal' : 'vertical'
     );
@@ -153,9 +166,43 @@
             {/if}
         </div>
     </div>
-    {#if $treeFileView}
+    {#if $treeFileView || $workspace?.folder}
         <Resizer orientation="col" bind:after={$rightPanelSize} minAfter={100} maxAfter={400} />
-        <FileList orientation="vertical" recursive={true} style="width: {$rightPanelSize}px" />
+        <div
+            bind:clientHeight={rightPanelHeight}
+            class="flex flex-col h-full min-h-0 shrink-0"
+            style="width: {$rightPanelSize}px"
+        >
+            {#if $treeFileView}
+                {#if $workspace}
+                    <div class="px-2 py-1 text-sm font-semibold shrink-0">
+                        {i18n._('menu.workspace')}
+                    </div>
+                {/if}
+                <!-- a row, as the file list was: its scroll area is as high as this, whatever its content -->
+                <div class="grow min-h-0 flex flex-row">
+                    <FileList
+                        orientation="vertical"
+                        recursive={true}
+                        style="width: {$rightPanelSize}px"
+                    />
+                </div>
+            {/if}
+            <!-- the open folder (the desktop app) under the files that are open -->
+            {#if $workspace?.folder}
+                {#if $treeFileView}
+                    <Resizer
+                        orientation="row"
+                        bind:after={() => explorerHeight, (height) => ($explorerPanelSize = height)}
+                        minAfter={60}
+                        maxAfter={Math.max(rightPanelHeight - 80, 60)}
+                    />
+                {/if}
+                <div class="flex flex-col min-h-0 shrink-0" style="height: {explorerHeight}px">
+                    <Explorer />
+                </div>
+            {/if}
+        </div>
     {/if}
 </div>