xMod ain't pretty, but it is an FM Synth with 3 oscillators and a surprising amount of features. Even rtpMIDI for wireless MIDI!
I can't find any specific details for this, nor examples. It just came out last night, but the developer hasn't updated their website since 2011! Here is the iTunes description:
xMod is unique both visually and functionally. The synth is a polyphonic triple-oscillator cross-modulated FM synthesizer with 32 preset patches (sounds). Synth patches are displayed in a "sound map" that gives the player the ability to quickly move from one preset to another. Tapping the SOUND button exposes the underlying synthesizer controls. Another set of 32 user patches can be programmed, saved, and shared.
Tapping the PLAY button reveals a built in MIDI player and audio recorder behind the keyboard. Download and play multi-track MIDI files. Using external accessories like iRig MIDI you can play xMod using an external MIDI control device. xMod also supports MIDIRTP so it can be played wirelessly from another device.
Could be interesting for FM hackers! We need more apps with Mod Matrixes. I like the way they've got all the knobs on a single screen, with the Matrix! The price is kind of high for a shot-in-the-dark-app like this, but it could be a diamond in the rough. Thanks to reader Paawo for bringing it to my attention!