Alithia Engine is a 3D game engine with world editor, gui system and dynamic scripting written in plain C, SDL and OpenGL with an emphasis on getting things done faster even if it goes against making things look pretty.
The engine has an embedded world editor which is actually just an engine mode. The scripting system can use editor functionality and unlike in many other game engines, the scripting is “always on” which removes the need to recompile and/or reactivate scripts and allows them to be modified while the game is running – from within the game.
There is enough documentation with the engine’s source code (and i will write certainly more) which can be found in the doc/ directory. You can view it by downloading the source or using the Source Code link.