Mobilesynth, by Allen Porter, is a free, an open source synthesizer, targeted initially for the iPhone. It’s a free download in the App Store.
Because Mobilesynth is open source, it’s available for other developers to reuse and repackage.
Johnnyg0 notes, at PalmSounds, that these apps are based on the open source MobileSynth:
- Core Synth
- Moogie Synth
- OL Synth
- iSynthesizer Pro
The apps vary in how much they add beyond what’s in the original Mobilesynth.
There are both commercial and free variants. So, if you see a commercial Mobilesynth variant, make sure it adds something useful, so you don’t find yourself buying the same synth multiple times.