iOS Musician Apps (113) Supported Technologies is Inter-App Audio (IAA), Instrument Sounds is Keyboards

Lagrange synthesizer has two oscillators, a noise generator and two filters that can be selected from various algorithmic models.

Mersenne is a melodic percussion synthesizer that combines two FM synthesis modules, a noise generator and a resonator.

Redshrike is a polyphonic synthesizer that combines a resonator designed to make more complicated sound creation and subtraction synthesis with an FM oscillator that creates violent distortion.

Lorentz is not only a live-oriented analog modeling synthesizer, but also has a resonator that makes metallic and aggressive sounds.

Laplace is a physical-modeling synthesizer based on resonator synthesis that makes it easy to create bowed string, plucked string, blown pipe and metallic sounds.

GSi VB3m simulates the famous american tonewheel organ better known as the Hammond Organ B3.

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

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

Play with the sound of a full cathedral organ, created by award-winning sound designer Kurt Ader.

Colossus Piano sets a new standard in terms of realism, detail and overall quality of piano sounds on your iPad, iPhone and iPod touch.

The second best sounding piano app in the App Store (after "Colossus Piano")!

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.

Englitina is an authentic-sounding English Treble Concertina for the iPad.

Phase84 is a phase distortion synthesizer.

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.

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

Elsa is a retro style sampling keyboard with tempo based looping.

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

This synthesizer emulates male voice vowels in a unique way.

Tines emulates an electric piano.