Icar, from Rob Lang.
Billed as a "Space Opera" (something I'll admit I double-checked to make sure I understood it right), Icar is not only free, but appears to be well supported. It has its own website, forum, blog, and is on its 4th (?) iteration.
I was really surprised by the blog. This appears to be a living, if not thriving game. If you like the genre, you should really check out the game.