AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Sampulator - Make (and record) beats on your keyboard
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.
Logic Pro X - Music production.
Radium - Radium is a music editor with a new type of interface.