Also an all-purpose editing tool for Quake/Q2/Q3 engine game editing. Originally started as a level editor for Quake, named QuakeMap. Then expanded to be a model editor, level editor, pak editor, and various other handy utilities/features were added. It's a freeware program, and highly recommended, although it is taking a while for full Q3 support.

Freeware by Armin Rigo, and is currently open-sourced on Sourceforge