Ask HN: Are there opensource alternatives to backend services like Parse?

There are many useful services for building web and mobile backends (Parse, Kinvey, StackMob, Storage Room and others). Does anybody know if there are opensource solutions than can be used to self-host a simple backend? Of course I'm not expecting something with the same level of features (i.e. without notifications), and I know you can code a very basic backend with Sinatra, Flask and so on, but I'd like to know if an opensource user/data backend administration with relevant API exists.