In the cause of the years I worked on a number of Apps for the iPhone, iPod touch and iPad.

Some were "internal" only -meaning I cannot tell you more about them here-, but quit a few of the others even made it to the App Store at some point:

Tetsuki, a realy cool Go (Baduk, WeiQi, ...) playing client.
Allows you to play on the PandaNet IGS (Internet Go Server) as well as playing, or noting (writing down, recording) your own games on your iPad or iPhone.
DieSchulApp, allow kids, parents and teachers to keep in touch.
Targeted to RealSchulen and Gymnasien bringing homework, changes in the kids their schedules and school events directly on your iPhone.

Last I checked all were still available in the AppStore, that might have changed by now, of course ...