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.
VTK.NET is a .NET wrapper for the Visualization Toolkit. With it, you can write Windows Forms applications in C#, managed C++, Visual Basic, or J#. It includes a Windows Forms Control for drag and drop design of forms.
The Anvil is setting out to produce one strong platform for all media. Fluid work with major audio, video, raster/vector images, 3D formats and scripting languages will allow us to start from anywhere and temper out the masterpeice we needed.