I'm looking for a great full-featured 2d/3d game engine (high-level rendering, physics, animations, etc.). So far, my progress with SFML and OGRE have been slow, and I'm looking to rewrite my application (an IDE) on top of a high level full-featured engine. XNA based seems very attractive, but is not a requirement.

I would like as little red tape as possible (a very very permissive license, allowing users to create and distribute applications developed by my application. Not necessarily free, but free and open source usually satisfies the categories).

The language of choice would be C#. Here are a couple that seem very attractive to me:

Synapse SunBurn Engine (afraid of licensing issues) <- Most attractive
Tomahawk (XNA based engine, no 4.0 support. 3D only, but probably could be used for some 2D rendering)
Ox (Another XNA based engine. Outdated.)

Any ideas?

Torque, if you're really for an engine to build off of. Has a C++ style scripting(oop) so I guess c# would apply to this.