skippy-xd (full-screen task-switcher)

Skippy-XD is a full-screen task-switcher for X11.

You know that thing  Mac OS X,  Compiz  and  KWin do where you press a
hotkey and suddenly you see miniature versions of all your windows  at
once? Skippy-XD does just that. It's most commonly known by Mac OS X's
name for it - Expose.