Pulse Code the makers of Rhythm Studio have released Modular Synthesizer for iOS. The synth is free and then you buy modules for .99 each or $4.99 for all the current modules available. It certainly wont sound as sharp and wild as the real thing but should be great fun on a flight, waiting room or while on the phone with your mother in law.
“Modular looks, acts, and sounds like a hardware modular synthesizer to give you features that musicians want such as pulse width modulation, oscillator sync, 4 pole ladder filters, and 1v/oct filter tracking. Traditional modular systems are expensive and out of reach for the average artist. Modular is here to bridge that gap and allow everyone the opportunity to use these powerful synthesizers.” – pulsecodeinc.com
For more info: pulsecodeinc.com/modular