Sometime back, I had authored WS-Sudoku that was a game of Sudoku built using Windows Communication Foundation (WCF) to illustrate multi-player gaming using callbacks over WSDualHttpBinding.
This was subsequently modified by the WCF Team to leverage the three pillars of WinFX: WPF, WCF and WWF. It has been made available for download, with its source code, for you to see the richness of WinFX as a developer platform.
Download it from here.
Inside and Out... 