http://fractalsoftworks.com/
It's top-down 2D though, so it's not something that could be called a "sim".
Current Features
Pilot your ship in top-down 2d combat
Command your fleet in tactical battles
Detailed combat mechanics
Customize your ship’s loadout before battle
Explore a war-torn star system
Mod support for user-made factions, missions, ships, and weapons
Upcoming Features
Play your own character who gains experiences and upgrades skills
Hire officers to give skill bonuses, pilot auxiliary ships, and oversee your operations
Explore the sector for knowledge and profit
Trade goods, run mining operations, build industries — and defend your interests
Become involved in factional politics
Sounds to me like Sid Meier's Pirates! in Space, though a lot more involved. Doesn't quite look like you'll be marrying the daughters of governors, so it seems low on the charm -- though the 2D art is pretty good.
http://www.youtube.com/watch?v=foklpwLu7v8
Most exciting of all the upcoming space-themed games because it's definitely not an MMO.
