AstroRaid
Arcade style vertical shooter set in space. Battle through alien forces to deliver a vaccine to earth and save the human race.
Planetary Defense
Arcade-style planetary defense game. Its features include its small footprint, multiple difficulty levels, and several weapon types. Available for Windows in several languages.
PoMPoM Games
Free demo and purchase of Mutant Storm and Space Tripper for PC, Mac, and Linux.
RedEagle
First/Third person futuristic game featuring single- and multiplayer modes. Requires a PowerPC running Macintosh Classic (Systems 8 and 9, or OSX in Classic mode.)
Space Invaders for DirectX
Clone of the classic arcade game Space Invaders.