I'm giving a presentation on FSM.NET at the local users' group on Monday night. @dahlbyk is opening for me, so I've got a tough act to follow.
My first open source project on GitHub is FSM.NET, a simple "stateless" finite-state machine library for .NET. It's also available through NuGet.
The library is written in F#, but is designed to be easily callable from C#. The project includes examples in both languages.