Freespace 2

[Banedon]

This old game won lots of accolades, and since then its fans have gone on to make many custom campaigns for it. The game itself costs a few dollars, but beyond that all the extra content is free. FS Open (the program used to get these mods) used to be hard to install, but with Knossos, it's gotten a lot easier. Would definitely recommend to anyone who hasn't tried it, it is after all only a few dollars for hours upon hours of playtime.

[Marzhin]

My favorite space sim. I wish they'd do a Freespace 3 to continue the story, but it's unlikely as Volition is now a very different company (and I'm not even sure they still have the rights for Freespace anyway).