irrEdit
realtime 3D world editor
irrEdit was an extensible free realtime 3D world editor and radiosity lightmap generator.
It can be used as editor for games and 3D multimedia applications. irrEdit has been written to be used with the open source Irrlicht 3D engine and can be customized and extended to be used as editor for your own applications.
irrEdit has now been replaced with CopperCube, which is also free.
You can buy the Source Code of irrEdit, if you like.
irrEdit has these features:
Scene, terrain, and particle system editor
Because irrEdit was created as full featured scene editor, it is possible to edit and place everything needed for games and multimedia applications.
Extensible
Includes a plugin and scripting system for extending the editor: C++ plugins as well as a Scripting API for adding new commands and tools to the editor
Light Map Generator
irrEdit has a fast built-in light map generator. This is useful for games with static geometry wich needs a fixed, nice looking lighting.