I'm the dev for an indie space game called "Salvation Prophecy". One of the players suggested I drop a post in here, since there's lots of space-sim and sci-fi fans around.
Salvation Prophecy has big space ship battles, planet battles, alien worlds to explore, and some military strategy at the highest rank of the game.
It's PC, indie, DRM-free, single-player, released on Desura and Gamersgate, and closing in on Steam greenlight. A quick overview:
4 playable character races
Screenshot: Docking at a Space Station
Screenshot: Invading an enemy planetary colony.
Screenshot: An alien artifact site.
Screenshot: Galaxy map and military strategy interface.
More features and info here:
Steam Greenlight page
Let me know if you have any questions, I'd be happy to answer.