Recently I was telling my dad about FreeSpace 2 because he always liked the space sim games I had as a kid. A few years ago I discovered that FreeSpace 2 source code had been released for free, and apparently a free port of the game for Mac. I thought I’d look-up the download link again. MacUpdate has a link to the FreeSpace 2 Mac download.
You can also buy the PC retail version of the game from Good Old Games and extract the data files to install it on Mac using FreeSpace Open to play it (you will need access to a Windows PC to install and get to the game files).
FreeSpace 2 Source Code Project