A real-time client-side library that ties in to their database hosting service, basically. Also, if you want to have any non-realtime parts of your web app that do server-side processing of data then it looks like you have to use Node.js to talk to Firebase, as there's no REST API for it that I can see. I guess they don't mind because they're trying to get you to do all data processing in the client anyway. Definitel…
Also, there is a rest API and I believe they're working on clients for other platforms so that nodejs isn't the only player in town.