Three of them: The ServerConfigMOD download page has the source code for this Quake II mod that offers a bunch of configurable options to set up a multiplayer server. Action!Quake2 Server Launcher is a front-end to set up AQ2 servers meant primarily for LAN parties. Finally, Infos & Downloads zu Q-Start & Q2Start has a new version 2.1 of the Q-Start front-end for Quake (1), which is now freeware instead of shareware.