Area 51 is a rather good FPS from 2005. I’m asking that you rip the Gray alien model from the game.
It’s freeware for US-based users, but I’m pretty sure anyone can download it now.
But because Midway went under a while ago, the game isn’t supported and doesn’t work on Windows 7 or Vista- there’s a patch out there somewhere but even if you get it to start, on Vista and 7 it still has issues.
I’m having a hell of a time figuring out what engine it uses, but I’m fairly certain it’s Quake 2 or some variation of it.