I've had a quick look, and it looks like it's primarily a simple online database, with a basic push notification API. Obvious use-cases for the DB would be app

I've had a quick look, and it looks like it's primarily a simple online database, with a basic push notification API. Obvious use-cases for the DB would be apps that need to share data between phones (e.g. multiplayer games/high score tables/chat etc). You're right that it doesn't look like it's able to run any server-side logic, and if you need that you'll need a separate server, but it does provide what seems to be an easy way for that separate server to do things like send push notifications.