Back in 2010, I also ran my own project in this space called "Goggles." https://knowyourmeme.com/memes/sites/goggles It was a bookmarklet that turned any webpage into multiplayer MS Paint; viewers with the bookmarklet active could see others painting on the webpage in real-time, before websockets made this kind of interaction commonplace. The entire thing ran on a single-threaded nodejs instance, serving something like 1k simultaneous connections at peak. Every half-hour or so it would crash from memory leaks. Good times.
Moderation was the thing that killed my project. Some users became victims of targeted harassment campaigns; bullies would draw dicks, swastikas, nooses, racial epithets etc on their personal tumblrs or homepages. There's something insidious about knowing that folks could be graffiti-ing your own webpage behind your back unless you're constantly checking goggles, so it didn't feel right to keep the project running knowing I didn't have the motivation to add proper moderation tools and didn't want to build user accounts or any sort of reputation system to keep the UX simple.
Some folks made absolutely stunning pieces of art on corners of the web that nobody saw. I probably still have the shapefile database archived somewhere... maybe we could reunite artists with their work someday.