(commercial) Starfarer is a single-player sandbox style space role-playing game with strategic elements.
StarQuest - Sole Surviver
StarQuest: Sole Survivor is a starship combat game. You are the guardian of the solar system with the duty to protect earth from invading aliens.
Starry is a space shooter that is vaguely reminiscent of the classic X-Wing/Tie Fighter series.
Stellar Duel is a SVGA space ship game which features 640x480x256 graphics, full screen 2D game play, 3D rendered graphics, and sound.
(commercial) Two enemy races launch a devastating attack, foretelling the end of our world! The only chance for survival is to seek and destroy all enemy starships, which are the main threat. Read more
Syder Arcade is a free scrolling, multi directional shoot 'em up, an uncompromised old-school experience, furious, challenging, and straightforward.
Target Acquired is a top-scrolling space shooter which uses the Simple DirectMedia Layer.
Torus Trooper is an abstract shooter where you race against the clock as you pass though tunnels.
Tumiki Fighters is a side-scrolling shoot-em-up where you can salvage enemy ships, attaching them to your ship to give more firepower.
TuxFighter is an asteroid-like shooter written in python/pygame.
XPilot is a X11 based multiplayer space combat game. You guide a triangle shaped space craft through a two-dimensional cave-like environment. Your vehicle has a very simple steering system: a rear mounted engine provides forward propulsion, while two thrusters (one mounted on each side) are used to rotate. The space you fly through has no resistance, but plenty of gravity. Learning to fly is one of the most challenging aspects of XPilot.
Yar's Revenge is a rather wierd shoot-em-up game that originated on the Atari 2600. It's more fun than it looks.