http://github.com/joeyrobert/fiasco and http://joeyrobert.org/
Copyright © 2009-2010 Joseph Robert and licensed under the GNU LGPL.
Fiasco is an open source, pre-alpha chess engine written in C# and .NET. It features a "classic" alpha/beta brute force search and an opening book. It's built using a 10x12 mailbox board representation.
Developed on Windows 7 Professional using Microsoft Visual C# Express 2008 and tested on Ubuntu 9.04 using Mono 2.0.1 and MonoDevelop 2.0.