If you highly value the hosted PaaS aspects of Firebase then it's good to look at (they are one of the best in that space). If you're looking for an open-source alternative that can be hosted in your private or public cloud, check out Couchbase Mobile (full disclosure, I'm an architect at Couchbase). We're open-source under Apache 2 and have all the database and sync functionality of Firebase. Many of our customers/users evaluate us against Firebase, it really depends on where you place the most value: PaaS, controlling your own data, open-source, etc. http://developer.couchbase.com/mobile