IronRuby is a Ruby virtual machine implemented in C# as part of the .NET framework. It allows Ruby code to interact with .NET libraries and be deployed on .NET infrastructure like IIS. IronRuby provides interoperability between Ruby and .NET code, allowing Ruby code to consume existing C# code and libraries while extending .NET classes. Limitations include lack of support for native C gems and some rough edges in interoperability, but status is ongoing with links provided for more information.