What are some alternatives?
Splice Beat Maker - Make and share beats in your browser
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
Magenta Studio - Make music & art using machine learning
Psychosynth - Interactive modular synthesizer inspired by Reactable music system
Keezy Drummer - Make a beat in seconds
Wavepot - Wavepot is addictive music or beats maker platform that offers a live-coding environment for creating sound and music.