iOS Musician Apps (283) Supported Technologies is Inter-App Audio (IAA), Type is Instrument

Real Guitar is a realistic guitar simulator apps.

SK-51 is an all-in-one keyboard inspired by the Casio SK-1 (and his brother the SK-5), a 8-bit lo-fi keyboard from the 80’s, with sampling features and onboard drum machine.
Called the poor man's sampler at the time, this keyboard was a real instrument and has been used by many major artists such as Fatboy Slim, Portishead, Autechre and Nine Inch Nails.

BeatMaker is a drum sampler.

Harness the enormous power of 8 polyphonic synths: meet KASPAR Supersynthesizer.

Kauldron is a synth with new modeling technology, combined with features help you create aggressive synth sounds full of rich analog textures with the fewest knob tweaks.

Roxsyn is a metamorphic guitar synthesizer.

Galileo Organ 2 is a tonewheel and transistor organ app.

Pure Acid is a bassline synthesizer and drum machine in one app.

The ultimate orchestra sound app for sophisticated musicians by sound designer Kurt Ader, designed as professional sound module for your iPad, iPhone or iPod touch.

Oriental Strings is a professional sound module app for oriental keyboard players and for musicians who simply want to resemble the typical sound of the Middle East in their songs.

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

This app contains the following instruments: Trumpet, Trombone and Saxophone sampled in four different brass sections.

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.

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

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

Mynth is the new intuitive and powerful synthesizer by Fingerlab.

This app is a portable multitrack audio and MIDI recording studio featuring virtual instruments, editing with unlimited undo/redo, mixing, real-time effects, automation and much more!

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