I made this a few weeks ago but forgot to share it.
Communol is an infinite canvas application that runs in real time using socket.io. This means you can go to the site at the same time as anyone else, and your changes will be automatically synced and visible as you draw!
I wrote all the code from scratch. I used the concept of chunk loading to load in visible portions of the canvas and json objects to load drawings in. I may change the database to something more efficient as the canvas gets more detail added to it.
I recommend opening in a new tab. Hope you enjoy!