Amnesia Length?

[Sexbad]

It's a map editor for custom single player levels. It's WYSIWYG and scripting is easy. There are also decal editors, model editors, and material editors for custom content.

A video of the level editor and a quick building of a room can be found here: http://www.youtube.com/watch?v=0XojVUZJPmc

It supposedly comes out with the game.