Vega Strike
This is an open source project for MacOS, Windows, and Linux. The universe seems quite expansive and in-depth, and the on-station interaction is good. However, the in-ship graphics are disappointing, the controls clunky, and combat system poor. In all fairness, this is not the full release and it is a work in progress that shows a lot of potential. I'd recommend keeping your eye on this one, but don't download it yet.

Vega Strike Home Page