Conquests is a turn-based 4X Civilization-like 3D strategy game for Windows and Linux. You can discover new technologies from the stone age to the space age, explore the world, and wage war on your opponents. It supports both Direct3D and OpenGL graphics, and can run in both 2D and 3D modes.
Turn based tactical battle multiplayer game with Aliens and Marines
Spaxe Hilk is a turn based tactical battle game, where marines battle it out against aliens. It's still early in development but coming on nicely. Spaxe Hilk is purely multiplayer and can be played with 2 or more people, depending on the mission.
Watch a preview: http://www.youtube.com/watch?v=NdWXLmkPlJ0
...It can be played in arbitrary-sized arenas, so there is no single solution, but a game of any size is a proper subset of all larger games.
This project produces a solution for any arena you select, provided you have time and disk space enough.