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

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

Moebius Lab is a multimorphic sound processor which contains a synth, a varispeed stereo sample player, effects and LFOs that can modulate each parameter.

Pure Synth® Platinum is a full-blown rompler/synthesizer for your iOS device. Neither the synth engine or the sample engine is an afterthought: Both engines are fully capable and feature-rich. The romper section contains a well rounded assortment of analog, synth, string, digital, and acoustic instruments.

Professional Virtual Analogue Synthesizer.

Historic Harpsichords - Ruckers 1628 is a sampled recreation of one of the greatest and most valuable harpsichords of all time.

SpringSound is a physical-modeling audio synthesizer that produces sounds by simulating interactions and vibrations of a set of activators and masses connected to springs.

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.

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.

Poison-202 is a professional Vintage Midi Synthesizer.

miRack is a Eurorack-style modular synthesizer. It aims to provide user experience and audio quality close to those of the real Eurorack hardware.

Neo-Soul Keys® Studio 2 is the next evolution in electric piano sounds and effects from Gospel Musicians, which features a complete architecture overhaul using our new Pure Synth® structure and licensed VKFX effects.

LayR is a polyphonic, multi-timbral synthesizer for iPad and iPhone, delivering up to 256 voices of rich, multi-layered and textured sounds.

Continua is a three-oscillator / dual-filter six-voice virtual analog synth, with fully polyphonic modulation sources and built-in custom-designed effects, for everything from complex, evolving chill-out soundscapes to New Wave synth stabs.

Thanks to it's true VA synthesis engine, the use of analog-modelled non-linear filters and extensive modulation options, Flowtones sounds warmer and more analog than digital romplers and wavetable-based synths.

Arctic Pro Synthesizer / Vocoder is a modern subtractive synthesizer.

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

The Minimoog Model D App is a mobile transmutation of the world’s first portable synthesizer, the Minimoog Model D®.

The Moog Model 15 App is the Moog modular synthesizer and synthesis educational tool.

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

FM TiNES is an electric piano library dedicated to the most beautiful FM electric pianos ever made.