Roland 808303.studio - TR-808 drum machine and TB-303 bass synthesizer emulator
Sampulator - Make (and record) beats on your keyboard
Splice Beat Maker - Make and share beats in your browser
Audulus - A universe of sound at your fingertips - Audulus is a modular music processing app
BlokDust - Join blocks together to build sounds with this web-based music making app.
NodeBeat - Make music with NodeBeat, the intuitive and fun visual music app for all ages.