http://labs.dinahmoe.com/plink/
via https://www.html5rocks.com/en/tutorials/webaudio/intro/ "Further listening"
Seriously, makes me feel like a kid again, such simple joy, INSTANT joy! At one point I had 4 other strangers improvising with me, it felt like a Jazz open stage but EDM, kinda. And at times we were harmonizing, or intentionally trying to be in contrast with other, etc... Felt like community, joined with strangers by music only. :-D
Almost* as fun: a "soundtrack" generator http://labs.dinahmoe.com/theme
and this LEGO-block-music thingie http://labs.dinahmoe.com/tonecraft
*ALMOST.