Shameless plug ahead...
I've made a Picross game for webOS devices. (TouchPad, Pre, Pixi, Veer...) It also runs happily in a modern web browser, including those on iBerry and BlackDroid and AnPhone and whatnot.
The idea behind the game is that the process of solving a puzzle, using numerical clues, creates a pixel-art picture. I didn't invent Picross; someone much more clever did. But, I turned the idea into an HTML5 toy, and spent many insomniac hours thinking up 8x8 pictures, then testing and re-testing them to guess at their difficulty and make sure the clues weren't ambiguous. I recruited some help too; my wife contributed a handful of puzzles, as did a coworker and an enthusiastic early adopter.
Like all my little pet projects, it's open (GPL3) and you're encouraged to peek inside and learn from or build on it. I do sell the 99-cent webOS app with all of the (384, but who's counting) puzzles and the builder tool enabled, but when I say it's open I mean it - it's not hard to enable that stuff anyway if you're broke/cheap/webOS-less. :^) For BlackBerry PlayBook users, I'll probably release the game and demo in the BlackBerry store too at some point, but for now the web version runs very nicely.