(Disclaimer: I work for Fanout)
If you want to add realtime to an existing project that already has a database, then I suggest checking out Fanout ( https://fanout.io/ ). We intentionally don't want to own your whole stack, and we've opened our code and protocols so that you're never trapped. Would love to get your feedback.
https://www.loggur.com is like Firebase on steroids, though only launched a few weeks ago. There is a lot to come: first thing being proper documentation for the REST API behind Loggur (should developers prefer to talk directly to it), and then hopefully huge strides in usability. But we need tons of feedback for the latter!
Re:Firebase is Joining Google
by reshambabble on Wednesday October 22, 2014 @10:32AM
(#8492857)
Parse actually seems pretty developer-focused. So does Syncano, except their free tier is limited. I believe they're changing that, though. Pubnub, Kinvey, etc. all seem to target more enterprise clients.
As for the open source solutions, I specifically want to pay someone money to solve this for us. We've been running ShareJS, but it's annoying to maintain and fix.