For a few years now I've been working on mg2modeller. https://sourceforge.net/projects/mg2modeller/
Mg2modeller is an attempt to recreate Caligari TrueSpace on Windows/Mac/Linux. I've been writing the program in C up until now, but I am looking to switch to C++. I've been using OpenGL, and am currently rewriting the geometry engine to use OpenGL 4.