GtkRadiant is a level design program developed by id Software and Loki
Software. It is used to create maps for a number of computer games.

GtkRadiant originated as Q3Radiant, the Quake III Arena level design tool,
which was a Windows-only application. Two major things are different in
GtkRadiant: it is based on the GTK+ toolkit, so it also works in Linux and Mac
OS X, and it's also game engine-independent, with functionality for new games
added as game packs.

GtkRadiant is an Open Source application. Source code is publicly available
from id Software's Subversion repository and new additions to the code are
covered under open source licenses. The core Q3Radiant code, however, was
originally under id Software's proprietary license. The license for both the
editor and toolset (notably Q3Map2, the BSP compiler) was changed in February
2006, and publicly released under the GPL on February 17.

More up-to-date fork, NetRadiant, is available as `games/netradiant' port.