Xpenguins makes cute little penguins fall from the top of your screen and walk on the top of your windows under X11.
Release Notes: New themes ("Bill" and "Big Penguins"), a new "--squish" option allows you to kill the penguins with your mouse, any number of themes can be run simultaneously, and overwritten desktop icons are redrawn.
Release Notes: Functionality with KDE 2, Nautilus, and a number of other desktop environments/window managers that put a big desktop window over the root window, and the XPenguins GNOME applet is themable.
Release Notes: Twice as many penguin types, and themeability support (instead of penguins, you can see turtles, the Simpsons, Sonic the Hedgehog, or Winnie the Pooh).
Release Notes: Initial freshmeat announcement.