Once upon a time, I embraced those ubiquitous, head-wrecking puzzles called Sudokus, and built a super-simple Sudoku Solver demo in ASP.NET 2.0.
In a recent article on MSDN, Stephen Toub has upped the ante significantly, by turning Sudoku into a demo for how to optimize Ultra-Mobile PC applications for touch and ink interaction. This is a very thorough article that covers a lot of ground in the APIs and also features a very polished sample app!
The only thing that would be cooler than solving the Sudoku in the free morning newspapers they give out on the Luas tram here in Dublin would be solving it on my tablet PC, using ink. Did I say cooler? I meant geekier. :)
[Note: The article's source code download contains a pre-compiled binary of the Sudoku application, but it only runs on Windows XP Tablet PC Edition 2005 or later.]