Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
Supabase - An open source Firebase alternative
restdb.io - restdb.io lets you create databases and REST APIs quickly. Development databases are free. Powerful web-based and mobile-friendly data management.
PubNub - PubNub is a real-time messaging system for web and mobile apps that can handle API for all platforms and push messages to any device anywhere in the world in a fraction of a second without having to worry about proxies, firewalls or mobile drop-offs.
RemoteStorage - An open protocol for per-user storage OWN YOUR DATA
Nhost - Firebase alternative (open-source) with GraphQL