LinRadiant is a level (map) editor for FPS games that use id Software's engines (Quake 1/2/3). It is a derivative of NetRadiant with an improved build system. It is very easy to build, even for people with little experience in software development. It has built-in support for the following games: Darkplaces, Wolfenstein:ET, Nexuiz, OpenArena, Quake, Quake 2, Quake2world, Quake III Arena, Q3MIN, Tremulous, Warsow, and Xonotic. The package contains a lot of useful documentation (mapping tutorials, technical documents, etc.) that are automatically installed and can be accessed from within the editor.
The Brick Engine is a fast and simple lo-fi gaming engine. The engine provides a comprehensive API, including dazzling visual features, song playback, and collision detection: everything you need to make games with quickness and ease. The engine provides a straightforward C API and has language bindings for Tcl and Pascal, with support for more languages on the way.