Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
Ableton Live - Ableton makes Push and Live, hardware and software for music production, creation and performance. Ableton´s products are made to inspire creative music-making.
Sampulator - Make (and record) beats on your keyboard
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
Splice Beat Maker - Make and share beats in your browser