Absolutely brilliant editor! I use it for my projects - https://writingstreak.io and https://nulis.io.

I've also recommended http://letterpad.app/ to use it and they've switched to it now.

I'm a huge fan, it's insanely powerful and customizable, you can build anything you want with it.

The only problem is lack of documentation and tutorials, it's really hard to figure out how to use it beyond the very basics (for me at least). They do have a great community in the slack channel, they've helped me a lot, but better docs would make a huge difference.