I've played around with Jasuto modular synthesizer for a while; however, I had bought it before the creator had released the pro version. Eh. It was still lots of fun, but I was missing a few key operations which I wanted, particularly an operation that converted a signal to a control value.
Jasuto Pro recently lowered its price to $1.99; so, of course, I bought it, being the cheap bastard I am. I remembered that it is an amazing little synth builder. The range of modules is wonderful, and the wiring procedure is nice. Being used to MaxMSP, I often wish that there was a simple way to analyze the signals - something like the [number~] object in MSP, or at least some sort of oscilloscope. There is, however, a visualization of the waves going in and out of each module; but this is a bit too small and inaccurate for my liking.
To give you an idea of the simplicity and feel of Jasuto, here is a simple FM synth:
The module cut off at the bottom is a simple speaker out.
A great thing about Jasuto is the motion control. The location of each object in respect to the other objects is able to control a parameter of the object. One is able to move around an object, and loop that motion. It's a great tactile method of parameter control that agrees with the touchscreen interface.
With the Pro version comes the ability to control objects with OSC input. This is great, but I really wish Jasuto would include backgrounding, so that I could use TouchOSC on the same device for on-the-go testing...
All in all, though, a great modular synth for iOS. If you know your stuff, this will be a great tool for sound creation. Even if you're new to synthesis, a look at some of the documentation and the examples will have you making cool sounds in no time.