NRefactory supports analysis of C# source code: it includes a parser, abstract syntax tree, type system, semantic analysis (resolver), code completion, and several refactorings.

• Project Page (github)
• Bug Tracker
• NuGet Package: ICSharpCode.NRefactory
• Introductory documentation: Using NRefactory for analyzing C# code (on CodeProject)

Who uses NRefactory:

• SharpDevelop 5.0
• MonoDevelop 3.0
• ILSpy
• Saltarelle: C# -> JavaScript compiler