Space Exploration: Serpens Sector is a very long-running project to make a space exploration game in the vein of Strange Adventures, Star Control, and others. It's gone through a number of iterations and refinements over the years. In its current state, it is now gameplay-complete. The gameplay focuses on making interesting decisions balancing risk, reward, limited resources, the morale of your crew, and your reputation with the alien factions of the sector. The gameplay does not focus on combat.
SpaceZero is a RTS 2D space combat game for two players over a network. The objective is to conquer the space, defeating all enemies. At the starting point, you have only one ship and one planet, but you have money to buy more ships to conquer more planets. All the ships can be controlled by the computer (automatic mode) or by the player (manual mode). You can easily change among your ships, controlling all of them independently.
Stratagus is a cross-platform real-time strategy gaming engine. It includes support for playing over the Internet/LAN or playing a computer opponent. The engine is configurable and can be used to create games with a wide range of features specific to your needs. Some games based upon it include Battle of Survival, Wargus, and Battle for Mandicor.
Tactics Squad is a real time tactics game in which the player controls a squad of soldiers in a futuristic environment. Its main focus will be gameplay more than aesthetic pleasure. In other words, the main idea behind the game is not to astonish the player with audiovisual effects. Instead, the player should have a lot of fun.
"The Game" is a project designed to simplify the process of producing any high-quality cross-platform 2D or 3D graphical computer game. The hope is that any game can be produced simply by changing a few settings and pressing a "compile" button. The project has three "deliverables": a game engine library to abstract across the set of all possible computer games (applying object-oriented design methods to the general problem in such a way as to be usable in specific instances); a graphical interface for easy game design (an exercise in human interface design); and a gaming package with a lot of shiny games to play.
Tremulous is a computer game that blends a team-based first-person shooter with elements of realtime strategy. The objective of the game is to annihilate the opposing team. This is achieved by eliminating the opposing players and removing their ability to respawn by destroying their spawn structures.
UFO: Alien Invasion is a squad-based tactical strategy game in the tradition of the old X-COM PC games, but with a twist. This game combines military realism with hard science-fiction and the weirdness of an alien invasion. The carefully constructed turn-based system gives you pin-point control of your squad while maintaining a sense of pace and danger. The story is set in the year 2084. You control a secret organization charged with defending Earth from a brutal alien enemy.