The BSP map editor for Quake 1 and Quake 2 has been released as open source, thanks to it's original creators and inquiries by Goldenboy. Reckless has ported the source to the CodeBlocks Advanced IDE/ mingw compiler. Read the thread at Inside3D. Download link for current version: http://code.google.com/p/realm/downloads/detail?name=bsp-0.96e-opensource-v3.7z&can=2&q=
Features include fast rendering even with big maps, displays mdl and md2 models (instead of a box), translucent brushes for clip and caulk.
This screenshot shows the map APSP2, Plumbers Don't Wear Ties (But They Do Carry Shotguns) by Than. http://than.quaddicted.com/