TouchOSC is a modular OSC and MIDI control surface for iPhone, iPod Touch and iPad by hexler.
It supports sending and receiving Open Sound Control and MIDI messages over Wi-Fi and CoreMIDI inter-app communication and compatible hardware.
The application allows to remote control and receive feedback from software and hardware that implement the OSC or MIDI protocols such as Apple Logic Pro/Express, Ableton Live, Renoise, Pure Data, Max/MSP/Jitter, Max for Live, OSCulator, VDMX, Resolume Avenue/Arena, Modul8, Plogue Bidule, NI Traktor, NI Reaktor, Quartz Composer, Supercollider, vvvv, Isadora and many others.
The interface provides a number of customizable touch controls to send and receive messages:
Additionally the program can send Accelerometer data. The application comes with example layouts and completely custom layouts can be constructed using the free TouchOSC Editor application.
Please see https://hexler.net/touchosc for more information, video demonstrations and download the free layout editor application for macOS, Windows and Linux and the free TouchOSC Bridge utility to easily control any MIDI-capable application on your computer.