NUnit is a powerful open-source testing framework for .NET developers. It’s a great tool for unit testing, and supports a wide range of .NET languages, from C# and Visual Basic, to F# and IronPython. It has a great feature set, including test coverage, test execution reports, and integration with Visual Studio. It’s easy to set up, and provides excellent documentation and community support. If you’re a .NET developer looking for a robust testing framework, then NUnit is worth a look.