diff --git a/desktop/src/app/services/window-manager.service.ts b/desktop/src/app/services/window-manager.service.ts
new file mode 100644
index 0000000..7c4138f
--- /dev/null
+++ b/desktop/src/app/services/window-manager.service.ts
@@ -0,0 +1,145 @@
+import { Injectable, signal, computed } from '@angular/core';
+
+/** Represents an open window on the desktop. */
+export interface WindowState {
+  id: string;
+  title: string;
+  icon: string;
+  /** Which built-in app or remote session this window shows. */
+  appId: string;
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+  minWidth: number;
+  minHeight: number;
+  zIndex: number;
+  isMinimized: boolean;
+  isMaximized: boolean;
+  isActive: boolean;
+  /** Session id if this is a remote display window. */
+  sessionId?: string;
+}
+
+let nextWindowId = 1;
+let topZIndex = 100;
+
+@Injectable({ providedIn: 'root' })
+export class WindowManagerService {
+  /** All open windows. */
+  private windows = signal<WindowState[]>([]);
+
+  /** The currently active (focused) window. */
+  readonly activeWindowId = signal<string | null>(null);
+
+  /** Computed list of non-minimized windows sorted by z-index. */
+  readonly visibleWindows = computed(() =>
+    this.windows().filter((w) => !w.isMinimized).sort((a, b) => a.zIndex - b.zIndex),
+  );
+
+  /** All windows for the taskbar. */
+  readonly allWindows = computed(() => this.windows());
+
+  /**
+   * Open a new window for the given app.
+   * @returns The window id.
+   */
+  openWindow(opts: {
+    title: string;
+    icon: string;
+    appId: string;
+    sessionId?: string;
+    width?: number;
+    height?: number;
+  }): string {
+    const id = `win-${nextWindowId++}`;
+    const offset = (this.windows().length % 8) * 30;
+    const w: WindowState = {
+      id,
+      title: opts.title,
+      icon: opts.icon,
+      appId: opts.appId,
+      x: 120 + offset,
+      y: 60 + offset,
+      width: opts.width ?? 800,
+      height: opts.height ?? 520,
+      minWidth: 300,
+      minHeight: 200,
+      zIndex: ++topZIndex,
+      isMinimized: false,
+      isMaximized: false,
+      isActive: true,
+      sessionId: opts.sessionId,
+    };
+
+    // Deactivate all others.
+    this.windows.update((list) =>
+      list.map((win) => ({ ...win, isActive: false, zIndex: win.zIndex })),
+    );
+
+    this.windows.update((list) => [...list, w]);
+    this.activeWindowId.set(id);
+    return id;
+  }
+
+  /** Close a window by id. */
+  closeWindow(id: string): void {
+    this.windows.update((list) => list.filter((w) => w.id !== id));
+    if (this.activeWindowId() === id) {
+      const remaining = this.windows();
+      this.activeWindowId.set(remaining.length > 0 ? remaining[remaining.length - 1].id : null);
+    }
+  }
+
+  /** Focus a window (bring to front). */
+  focusWindow(id: string): void {
+    this.windows.update((list) =>
+      list.map((w) => ({
+        ...w,
+        isActive: w.id === id,
+        zIndex: w.id === id ? ++topZIndex : w.zIndex,
+        isMinimized: w.id === id ? false : w.isMinimized,
+      })),
+    );
+    this.activeWindowId.set(id);
+  }
+
+  /** Minimize a window. */
+  minimizeWindow(id: string): void {
+    this.windows.update((list) =>
+      list.map((w) => (w.id === id ? { ...w, isMinimized: true, isActive: false } : w)),
+    );
+    // Focus the next visible window.
+    const visible = this.windows().filter((w) => !w.isMinimized && w.id !== id);
+    if (visible.length > 0) {
+      const top = visible.reduce((a, b) => (a.zIndex > b.zIndex ? a : b));
+      this.focusWindow(top.id);
+    } else {
+      this.activeWindowId.set(null);
+    }
+  }
+
+  /** Toggle maximize for a window. */
+  toggleMaximize(id: string): void {
+    this.windows.update((list) =>
+      list.map((w) => (w.id === id ? { ...w, isMaximized: !w.isMaximized } : w)),
+    );
+  }
+
+  /** Update window position and size (from dragging/resizing). */
+  updateWindowGeometry(id: string, changes: Partial<Pick<WindowState, 'x' | 'y' | 'width' | 'height'>>): void {
+    this.windows.update((list) =>
+      list.map((w) => (w.id === id ? { ...w, ...changes } : w)),
+    );
+  }
+
+  /** Update window title. */
+  updateWindowTitle(id: string, title: string): void {
+    this.windows.update((list) => list.map((w) => (w.id === id ? { ...w, title } : w)));
+  }
+
+  /** Get a specific window's state. */
+  getWindow(id: string): WindowState | undefined {
+    return this.windows().find((w) => w.id === id);
+  }
+}