In 2013, I made a voxel editor that used some of the usual stuff like octrees and marching cubes. Voxel updates were multi-threaded on the CPU, but GPU would be a better choice I guess… Even if I used marching cubes, I kept the blocky look because I love it. Maybe I’ll go back to it !

The rendering is part of a home made engine, and the editing tool itself uses Qt.

There are some screen shots:

And here’s an early dev video: