Check out backendless.com, a complete alternative for Firebase with a freemium plan. Includes object database with support for relations and SQL-based searches. Native SDKs for iOS, Android, .NET, JS as well as REST. Supports push notifications and pub/sub messaging. You can augment server-side logic with your own server-side code (in Java and JS) and you can develop your own API Services. There is integration with AWS Lambda and very nice developer console.