Click here to see Shape Puzzle on the App Store.
Until it fell out with the outdated operating system on my iPad, I loved this for gentle vocabulary building.
The premise is that you choose a theme (e.g. Farm, or Under the Sea). You then have to make jigsaws of some nouns on that theme (e.g. Farm animals). The charm was that it would say the word for the thing your child touched. Which basically made this a very motivating flash card delivery system.