ILSpy is a free and open-source .NET assembly browser and decompression tool that is pretty popular in the C# development field, developed by ICSharpCode (i.e. the development team of SharpDevelop). It has the user interface, layout, and decompilation functions similar to Red Gate Software's .NET Reflector. Moreover, sometimes for some assemblies that can not be decompiled with .NET Reflector (because of encryption), it's still possible to do that using ILSpy. Simply speaking, it has only one purpose - to finally completely replace .NET Reflector and do better.