Wikipedia
csUnit is a unit testing framework for the .NET Framework. It is designed to work with any .NET compliant language. It has specifically been tested with C#, Visual Basic .NET, Managed C++, and J#. csUnit is open source and comes with a flexible license that allows cost-free inclusion in commercial closed-source products as well.
csUnit follows the concepts of other unit testing frameworks in the xUnit family and has had several releases since 2002. The tool offers a native GUI application, a command line, and addins for Visual Studio 2005 and Visual Studio 2008.
Starting with version 2.4 it also supports execution of NUnit tests without recompiling. This feature works for NUnit 2.4.7 (.NET 2.0 version).
csUnit supports .NET 3.5 and earlier versions, but does not support .NET 4.