Not only can most apps see the titles of all other open windows on the system, but they can log all your keystrokes, take screenshots, record audio/video of you or your screen, or copy/delete all the files in your home directory, without any explicit permission or notification.

This is at least true for Windows and most traditional (X11 at least) *nix systems.

That is one thing I think Android got right... by default it runs every application as a different user. That means different home folders and no visibility into other apps.