Excellent news from Synthtopia. The Mac OS app Audulus is on its way to iOS and the iPad in particular.
If you don't know about Audulus you should watch the videos below to get a feel for this synth building app, it's really worth a look at, and I think it is one of the few apps I know of that's moved from Mac OSX to iOS, which is an intriguing turn of events.
Anyway, have a look at the videos and also take a look at the Mac app on the Mac App Store too.
Audulus on the Mac App Store