Last year, Chris Sells wrote a series of articles in which he set out to rewrite Solitaire using Avalon. The lack of scaling graphics in the Win32 version (and lack of access to its source code, I suppose) forced him down the road of rewriting the app from scratch. Plus, the point was to explore "the initial decisions developers will make when building new applications targeting Longhorn." (This was before WinFX got decoupled from Longhorn and made available for Windows XP & Windows Server 2003.)
This year, I'm going to create a new WinFX-enabled version of Internet Hearts (the not-as-popular card game that also ships with Windows XP). But the focus is going to be on migration rather than starting from scratch. I'll gradually replace the UI with Avalon and the communication with Indigo. After all, I want to focus on the cool stuff; not rewriting the basic logic. I'll share results as I go along, and hopefully I'll be able to share the source code, pre-migration and post-migration!
I want to give special thanks to Steven Goulet (one of the folks on my new team), who came up with Internet Hearts as a great example application that could benefit from Avalon & Indigo. He also did the legwork of getting permission for the original source code. So without him, this would not be possible!