The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++. It is completely cross-platform, using D3D, OpenGL and its own software renderers.
QC++ is a code editor for QuakeC, the programming language for the popular game Quake. It is being developed in Visual Basic .NET and runs under any Windows version that supports the .NET Framework v1.0 (Windows 98, NT4, and newer).