iOS Musician Apps (117) Supported Technologies is Inter-App Audio (IAA), Instrument Type is Synth

iSEM is a recreation of the classic 1974 Oberheim SEM (Synthesizer Expander Module), one of the world's first self-contained synthesizer modules and the first to bear the "Oberheim Electronics" name.

Modulin is a customizable synthesizer. It allows for unique personal expression while providing a wide spectrum of visual feedback.

SynthMaster One iPhone is KV331 Audio's first full blown synth app for iPhone. It's a powerful wavetable synth with an intuitive workflow. With its simple layout, rich wavetable/waveform content and inspiring factory presets library, designing new sounds with SynthMaster One iPhone is a joy.

Shape is a polyphonic synthesiser allowing the user to draw the shape of the oscillator waveform.

Droneo is a synthesizer which drones with various timbres and precise intonations that blur the distinction between tones, timbres and chords. Its drone is great for meditation, centering, and calming,  walking and biking, but also can be set up for discordant noise and insect-like buzzing and chirping.

CHAiOS SYNTH 2 is a synthesizer/melody generator that creates unique melodies with just one tap.

Mynth is the new intuitive and powerful synthesizer by Fingerlab.

iPhilicorda is an emulation of a vintage organ from the sixties, the Philicorda, created by the Dutch company Philips.

Flynth is a synthesizer by Fingerlab, designed for musicality and easy use.

A Simple Ad-Free Piano-like Musical Keyboard. Easy to Play, Good Response and Small Application Size. Just Play the Instrument. The app doesn't use sampled real sounds but use FM synthesis. It sounds like piano though it's false.

Fed up with standardized presets and instruments? Feel lost in overcomplex filters and effects? Don’t wanna sound like everyone else? BLEASS is just the right instrument for you: it unleashes your inner musical creativity by bringing music production and performance to its very core: play, perform, compose beats and melodies in a new yet intuitive way thanks to its multitrack sequencer, synthesizer and drum machine.

LCW-2 mono is a little complicated synthesizer based on ToyTone and implements several experimental functions.

With this instrument you can transform any sound into a playable musical instrument via a technique known as Granular Synthesis.

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

Hexaglyphics is a 13-bit noise generator with an interface based on an original alphabet for hexadecimal values.

Wotja X is a new cross-platform interface for the 'Wotja Generative Music System'.

Groovebox is a free music studio app packed with synths and drum machines.

GarageBand is a DAW by Apple.

Electro-Harmonix, a pioneer since 1968 in the field of sound effects pedals for musicians, has produced an app which is a faithful digital re-creation of their circa 1980 analog cult-classic, The MINI-SYNTHESIZER.