Entropy Hits Steam Early Access
If space combat and interstellar trade interest you, take a look at Entropy via the MMO's Steam Early Access program, which has just begun.
Entropy is created by Artplant, the people behind Battlestar Galactica Online, and features more than 100 star systems to explore. The game is built around large-scale dog-fights and players working together for Entropy's mining, trading, and traveling components.
The Early Access program will let you play the game and provide feedback for the game's full release. If you purchase one of the founders packs, your character and stats can be rolled into the game when it officially releases. When that will be is unknown at this time.
Entropy is being developed for PC, Mac, and Linux. For more on the game and it's Steam Early Access program, head over here.
It will be interesting to see how the game's economy shakes out, as such player-controlled elements can be daunting to pull off successfully.