Kovel
http://github.com/aarroyoc/kovelKovel is a 3D voxel editor for Haiku, Linux and Windows. Create fantastic models without knowledge. Just fill the grid with your colors! Save your models in Kovel file (*.kvl) or in COLLADA DAE (only export). See changes in your models in realtime, rotate and scale. Kovel also has infinite undo history (in a same file). Kovel has a command line tool (kovelcli) to automate your work pipeline. Convert all your Kovel files into Collada DAE in a few commands.
It uses wxWidgets, OpenGL and libbson and it's made in C++.