Quake, Doom (1&2), Hexen, Heretic

Old games for OS X not only a nostalgia trip but actually quite a bit of fun.The DoomsDay engine is a enhanced version of the standard Doom engine for running Doom, Doom2, Heretic and Hexen. Fruitz of Dojo have a great Quake engine running up to 2560×1440 very smoothly on my iMac. Pick your resolution, set your controls, point the music to a good artist in your iTunes music folder and you’re set!

Note that you will require the data files. The shareware versions are freely available from most half decent ftp sites or directly from IDsoftware.