I've put up the files for the Fifteen puzzle I posted about the other day (here). This is an Xcode project (and includes a copy of the built application). It's on Dropbox (here).
You can move tiles by clicking with the mouse or using the arrow keys (much faster).
I have not solved the technical problem of eliminating unsolvable puzzles, but I've played a few times and have yet to run into one. Either my expectations are wrong or I'm just lucky. I'll try to work more on this some other time.