Interesting. How does one research this as home page offers a sign up only! I’m a bit wary of providing info to an unknown/undescribed service. Ah, not linked from home page is this Quarto – Publishing Basics which gives:
Is Quarto free to use?
Yes! Quarto is open source with a GPL-2 license. You can use or disseminate it any way that you would any GPL-2 licensed open source software.
So, force sign-up for a free service. What is the web coming to? 
But, that aside this looks like a web-based doc production service built atop pandoc. so, yes, interesting!
[digging further home page fail is a 404 on some JavaScript library as page has no content as is all generated on the fly. Hubris.]