Open Source Alternatives to Reflector?

Just to ask if anyone knows of an open source alternative to RedGate's Reflector? I'm interested in checking out how a tool similar to Reflector actually works. Note, if you know of a free but not open source alternative to Reflector, you can answer the following related question: - Something Better than .NET Reflector? Summary - Updated 11th May 2011 A quick round-up of the various open source projects and tools that have been suggested: - Common Compiler Infrastructure (CCI) - Mono Cecil - ILSpy - dnSpy (fork of ILSpy, project appears more active than original) - Dotnet IL Editor (DILE) - IL.View - Monoflector (no longer active as of April 2011) The following resources may also be of interest: - TypeView.cs - Jason Haley's notes on disassembling .NET - Adrian Bank's recent blog post summarising a number of Reflector alternatives, including several options not mentioned below. - Mark Lichtenberg's detailed blog post comparing several of the open source alternatives (DILE, ILSpy and Mono Cecil using MonoDevelop) to Reflector.