We prepared a webstart version of Jake2 on our homepage. Go ahead and try out playing Quake2 with just a mouseclick:
http://www.bytonic.de/html/jake2_webstart.html
There are three different links for the Jake2 because of problems on some hardware configurations. Try the links in that order until you find a working configuration. The webstart version runs without problems on Linux and Windows 2000/XP. The would like to get feedback from OS X users how Jake2 works on the Mac. Better would be a sponsor for a Mac so the can improve the OS X compatibility ourselves.
The webstart version allows the online installation of the Quake2 demo level data or the selection of a preinstalled baseq2 directory. Jake2 should work as multiplayer client against an original Quake2 server without extensions like nocheat.
Please send feedback to our Jake2 forum at sourceforge.
http://sourceforge.net/forum/?group_id=111156
Holger