MidiLooper.com

Ages ago I made www.midilooper.com to help people do live looping on their keyboards. This is the perfect simple webapp for musicians wanting to quickly start looping MIDI notes to make songs, and has many more complex features:
- Multi-track looping with volume and individually mutable tracks similar to a DAW
- Full MIDI mapping engine - control each aspect of the looper from your MIID device
- Offline mode - runs without an internet connection
- MIDI export
- Runs in a browser on Mac, Windows, Linux, Android (not iOS as webMIDI is not supported)
- Nice extras like midi monitor, undo/redo, instrument selection