Opened the link, went to the live app, read the first page of documentation and still doesn't know what this is.
Calls itself an "open source backend". A backend for what? Where does it fits in my application architecture? If it's a backend, can I write business rules in it? Is it a framework?
It's the first thing on the linked page:
Realtime database Authentication File storage Admin dashboard
I read their webpage instead of the first page of documentation and got a pretty good idea of what it was, perhaps their documentation is too in the weeds for the overview you’re looking for?
Personally I’d describe it as an alternative to firebase, if you’re familiar with that.