My son and I checked out a new app while the others were at the movie. It is called “Monster Physics”. You get to build contraptions to solve puzzles. We had lots of fun with it after we mastered the screen navigation… It has a very intuitive user interface and the puzzles are interesting. We made 2 separate players so we could each do the levels and compare our solutions. It is made by the same designer as “Stack the States”.
You can also create your own stuff free form. My son made a claw game.