iOS Musician Apps (115) Supported Technologies is Inter-App Audio (IAA), Instrument Sounds is Keyboards

Baervaag brings FM synthesis to the masses! An easy to use but still tweakable synthesizer, accessible to everyone.

AutoPad is an app for musicians that allows you to play ambient pad loops.

AutoArp turns your iPhone (or iPod Touch) into a musical instrument that is halfway between a traditional auto-harp zither and an arpeggiated analogue-style synth.

AudioKit Synth One is a completely free & open-source professional iOS Synthesizer. 

Free iPad instrument featuring the classic sounds of famous 80s FM Synthesizers.

Epic 64-voice Virtual Analog / PCM iPad Synth. Inspired by the Digital Synths of the 80s and 90s.

Arpeggist is a MIDI Note arpeggiator with a very flexible step matrix editor for programming and a unique “rolling dice” random arpeggio generator.

A matrix-controlled arpeggiator designed to play with your thumbs.

Arctic Pro Synthesizer / Vocoder is a modern subtractive synthesizer.

Combine 3 oscillators and a noise envelope to produce bright 80s-style synths, deep rich bass, punchy kicks and snares, a variety of screaming leads, and even breathy percussion.

Agonizer is a monophonic synthesizer designed in collaboration with YouTuber and synth bass expert Jakob Haq of haQ attaQ

Additive synthesis is a sound synthesis technique that creates timbre by adding sine waves together. The timbre of musical instruments can be considered to consist of multiple harmonic or inharmonic partials or overtones.

The unique dynamic wavetable synthesis allows you to explore an unprecedented wide range of sonic territory.

The hybrid synthesis algorithm on which Addictive Pro is based provides you with efficient means for easy control of complex sounds far beyond usual sound synthesis methods.

Accordion Vintage is a virtual sampled instrument based on an original Italian accordion made in Castelfidardo in the 60s years.