I'm just going to put this here and see what happens.
CubiQuake is open source GPL 3.0, and set up to be a framework for any cubic world project using the FTE Engine. (What people call voxels, which I've been informed is not the correct term for what people use it for, hence the name "CubiQuake".)https://github.com/uowaep/CubiQuake
Read the readme, and get FTEQW! (FTEQW revision 5424 or higher is required.)
The project is in early stages, but stable. View distance isn't super far, but it is decent, and by far good enough for a dungeon crawler. Let me know what you think, or if you want to work on the project.
Video of the editor:https://youtu.be/daxqYSIhHjQ