Some time ago i was looking for a good crowd simulation api for C#, i found sharpsteer but it was not stable (in terms of simulation accuracy) enough for my needs. The only one i found was RVO (really good one =P) that is written in C++.
I ported the RVO 2D version for XNA (works on Windows Phone 7) and created a wrapper for the RVO3D and RVO2 2D using C++/CLI.
Iam releasing the code of both.
The GitHub Project (Better option): https://github.com/tpastor/CSharpRVO
The XNA Version (just the .cs files)
The Wrapper (include the Source code of the original C++ and the C# code – RVO2 2D and RVO2 3D -> need to adjust some linkages to compile, i let them using absolute paths …)
The Wrapper DLL (Just add it to a .Net project, it uses exactely the same function names of C++ version. You can find usage demos in the source code provided in the above wrapper =P)
The usage examples for the XNA port of 2d can be found here (integrated with ploobsengine)