Source code available on GitHub
Tap/click to set add/change/remove arrow in a cell.
Play does automatic steps according to BPM.
You can share the url with your current 'song'. Changing size will randomize the field.
Advanced: Hold an arrow key or del/backspace while clicking.
This was inspired by Otomata - Completely re-done, hex grid and with web-audio that is generated on the fly!