While I have used desktop apps for music notation (for decades), I had kept an eye out for a tool that was cross-platform and potentially collaborative.
As we revise application code, government policy, etc. using source control tools, I have wondered -- licensing issues aside -- why it's not popular to collaboratively revise music.
I came across the abc notation standard a few years ago, but only recently decided to revisit the framework to give this Lightning Talk.
The most comprehensive resource I could find is here: https://github.com/paulrosen/abcjs
Recommended viewing: https://youtu.be/8yZSM4_-sgA