A .NET wrapper for Prof. Steven Johnson's NLopt nonlinear optimization library, version 2.2.3. Written in C++/CLI, it works with C# and VB.NET projects. I have only tested it with .NET 4.0
Full documentation of algorithms, etc. on the NLopt site. (Steven G. Johnson, The NLopt nonlinear-optimization package, http://ab-initio.mit.edu/nlopt)
To get started, see "UsingNLOptDotNet.cs". As per the instructions in the file's comments, noth NLOptDotNet.dll and libnlopt-0.dll must be in the directory where the code is executed. A project reference to NLOptDotNet.dll is required.
The wrapper source code is in "NLOptDotNet.h"