regarding b) conflict resolution Firebase presents a last write wins sync on an unsecured database, however, because the security language rules are dynamicall

regarding b) conflict resolution Firebase presents a last write wins sync on an unsecured database, however, because the security language rules are dynamically evaluated every write (with strong consistency), you are able to add other types of synchronization. For example, firechat[1] implements operational transforms, and this post[2] adds 2 phase commits. You have to figure it out yourself though which can be a fair bit of work. [1] https://www.firebase.com/blog/2013-04-09-firepad-open-source-realtime-collaborative-editor.html https://www.firebase.com/blog/2013-04-09-firepad-open-source... [2] https://www.firebase.com/blog/2014-02-04-firesafe-complex-security-logic-for-firebase.html https://www.firebase.com/blog/2014-02-04-firesafe-complex-se... regarding a) different types of sync, we recently added offline persistence, and there is also the REST API, but yeah, GCM sync would be nice to have and something we have been thinking about. (I am a Firebase dev)