This is a clone of the classic "Missile Command" Game, but it has better graphics and music. The gameplay has only been slightly modified. Penguin Command is completely licensed under the GPL.
Kraptor is a classic shoot 'em up scroller game, where you must fight against tons of bad dudes. This is a full game with massive destruction, powerful weapons, and high speed action in varied levels.
Works for Linux, DOS, Windows, QNX, Mac Os, etc..
Alex the Allegator is a series of games featuring everything from puzzle games to racing and platform jump n runs. The Alex games are provided with full source and are buildable on every platform that Allegro supports.