http://en.wikipedia.org/wiki/Jedi_Knight:_Dark_Forces_II
Quote:
Over time, unofficial editing tools were developed for this game; thus attracting a wide audience of level editors that still make levels for this game today. Countless modifications have been made to Jedi Knight by way of software products. Avid JK modders and fans have released new multiplayer levels, single-player levels, character models, and even weapons. The most reliable source of these mods is The Massassi Temple (http://www.massassi.net).
Think while it's still legal.