I wrote a seasonal iPhone app this year, and I thought the crowd here at HN may enjoy it, since it is all about engineering and physics. It's free too, which is always a good thing, right? http://itunes.apple.com/us/app/santas-engineer/id465563485?mt=8
I actually started it June 2011 to learn iOS, launched it in September, and have been steadily adding features and making improvements. It's something I use every day and I hope other people find it useful. Enjoy!
