Bungie, the same company that made HALO, has released the Marathon trilogy to the public! It is now possible to play these classic mac games for free (even IF you use windows). The Marathon trilogy is a space shooter released around the same time as Wolfenstein and Doom.

The main thing that sets it apart from those two games is its coherent, and I would say very good, storyline. The links below have everthing you need to get started:

Download link
Instructions for windows users
Marathon level guides

Hope you like it.