iOS Musician Apps (56) Instrument Type is Synth, Free

ChowKick is a kick drum synthesizer based on creative physical modelling of old drum machine circuits. The synth contains
useful parameters for adjusting the tone and fundamental frequency of the synthesized kick drum.

Accelerometer Synthesizer and Bluetooth MIDI Controller.

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

Jam Synth is a fully featured monophonic guitar synthesizer / multi FX for iOS.

Syntorial is a synthesizer training app, that will teach you how to program synth patches by ear.

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

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

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.

Aparillo is an advanced 16 voice FM synth tailored for complex sound structures , majestic motions, moving and evolving soundscapes and atmospheres that are perfect for film, TV or games.

TweakyBeat is a drum machine synth.

Made for complex and organic sounds, Factory sports a big modulation matrix with all kinds of features to create a wildlife of sounds. A vast array of DSP is ready to play: Analog style oscillators and filters, but also different flavors of wavetable synthesis, Wavetable driven Waveguide resonators and a 3-FX-Chain in a dynamic signal flow.

ToyTone is simple synthesizer. Select waveform, and move the slider. Tap the pad at bottom, you can play.

Spectrum is a collection of Audio Unit ports of popular eurorack synthesizer modules.

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.

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.

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

MonoStereo Synthesizer is a free full-featured analog mono synth with oscillator panning.

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

DRC is a virtual analog polyphonic synthesizer that recreates the characteristic sound of an analog synthesizer.