IronRuby is an open-source implementation of the Ruby programming language which is tightly integrated with the .NET Framework. IronRuby can use the .NET Framework and Ruby libraries, and other .NET languages can use Ruby code just as easily.
IronRuby is an excellent addition to the .NET Framework, providing Ruby developers with the power of the .NET framework. Existing .NET developers can also use IronRuby as a fast and expressive scripting language for embedding, testing, or writing a new application from scratch.
The CLR is a great platform for creating programming languages, and the DLR makes it all the better for dynamic languages. Also, the .NET framework (base class library, presentation foundation, Silverlight, etc.) gives developers an amazing amount of functionality and power.