Detune (the company who makes great synth apps with an ancient Korg hardware interface UI) made an independent, non-Korg synth app.
It’s called “I am synth” and it looks very much like Figure – pure digital interface, no fake knobs or wood panels. At first, it appears to be a simple chiptune-y thing, but watch the videos and it is apparent some serious FM crazy is going on under the hood. It’s like a Monotron but it sounds really good, is easier to use and turns into a phone when you’re done with it.
I Am Synth on the App Store – 99 cents
