Reflector is a tool for exploring and disassembling .NET libraries. From binary assemblies it will show you all the classes and their members including the relationships between them. It will also disassemble them back into C# or VB.NET source code; invaluable for understanding the behavior of objects but a nightmare if you feel the need to protect your source.
Ben Hall, UK MVP, C# expert and dynamic languages enthusiast has created a plugin for Reflector which makes it even more useful. Part of the power of dynamic languages is how easy they make exploration from the interactive environment. Ben has brought this to Reflector by embedding an IronPython interpreter (REPL). Whilst you are looking at the available methods and their arguments and return values you can actually instantiate classes and use them from the interpreter.
As well as being a useful tool the source code is another good example of embedding IronPython into a .NET application (plus how to write a Reflector plugin of course). In this article Ben explains how to use the tool and how it works under the hood.
It is great to be able to inspect the contents of an assembly with .NET Reflector, but to really understand the behaviour of code, it is nice to be able to call methods and see the results immediately within .NET Reflector. Now you can, thanks to the magic of IronPython and the DLR. Ben builds a REPL add-in for .NET Reflector and makes a great tool even more useful.