The application is included in Games.
From the developer:
ProQuake is JP Grossman's updated Quake client for Windows and Linux. This Mac version incorporates all the improvements of JPG's engine except cheat-free server connectibility.
ProQuake is the client of choice for the online competitive Quake players. All credit goes to JPG for ProQuake source code adjustments and Fruitz of Dojo for the Mac OS X Quake 1.1 port for which this release is based.
You may want to check out more Mac applications, such as GrapplingHookDemo, Worms 3D or Planet, which might be related to ProQuake.