Did you know the server-side mod Quake 2 Battleground was available for both IRIX and MacOS X? Well I certainly didn't. Apparently deleet ported and released this back in February, giving us another gem to add to the IRIX game library.
Visit the official Quake 2 Battleground web site for information on the mod itself, and then deleet's Quake 2 Battleground for MacOS X and IRIX to download the packages. If you don't already have Quake 2 you can download the IRIX version from SGI's Game page and the MacOS X version from Fruitz of Dojo.