Just played this game from the Santa Game Jam, it is truly a wonderful concept and it looks beautiful too! Great work! May I ask what engine you used? I find it interesting seeing what engines are out there.
Thanks for your nice words!
I don't like most engines because they are big and slow (in development and loading, that is), so I wrote the game from scratch in HTML5. I tried to separate some "Engine" part from the "Game" part, but gave up at some point. The downside is that it does not work perfectly with touch because I cannot test that very well...
I added a downloadable version to the page so you can look at the source more easily.
Edit: Well, I just found Bitsy. I like Bitsy. But I don't think I could have made PYD in Bitsy :(