In case you didn't know, the makers of the incredibly popular HALO series of video games started by making games on the Mac. Marathon is a first person shooter released around the same time as Doom (ID software), but for the Macintosh. It was famous for among other things, introducing the ability to mouse look. If you want to see their first games you can do that now. Mac (OS X), Windows and Linux, are supported.
Clike to download Marathon, Bungies first big hit:
You can find out more about Marathon on the wiki page here:
from Andrew Brett Watson.com