You can play online against a chess engine. Currently, three engines are available from increasing strength:
TSCP, Faile, Fruit.
The original source code was translated into C# for incorporation into Silverlight. That one from the TSCP is available on author's website (Tom Kerrigan). Two versions are available, one of which using pointers (faster but unsafe).
It should be noted that the C# version of the TSCP using pointers is as fast as the one written in Pascal (Delphi), which proves that C# can be powerful.
Your browser must have the Silverlight plugin update, version 5 or higher.
To bring diversity to the games played, a more important opening book is incorporated, it was created by Gabriel Leperlier.
The version of TSCP is the one of Norman Blais (tscp181null), incorporating the null move forward pruning.
To enlarge the chessboard, use the mouse wheel.