Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
Socket.io - Realtime application framework (Node.JS server)
Supabase - An open source Firebase alternative
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Etebase - Etebase makes it easy to build end-to-end encrypted applications by taking care of the encryption and its related challenges.
NATS - NATS.io is an open source messaging system for cloud native applications, IoT messaging, Edge, and microservices architectures.