[gimenete]

You can use http://backbeam.io It supports mobile-only development with SDKs for iOS and Android as well as web development and server-side logic.

Disclaimer: I work in the company behind it. If you have any questions we will be glad to help you out. By the way, the SDKs are Open Source and we are working on a "community" release of the backend for our customers to not be afraid of the vendor-locking.