Firebase!

GUN is an open source, realtime, graph database written entirely in JavaScript and built using peer-to-peer algorithms, making it surprisingly fault tolerant and easy to get started with.

Parse Server is a Parse.com API compatible router package for Node.js/Express.js.

Build incredible real-time applications in record time. Feathers is a real-time, micro-service web framework for NodeJS that gives you control over your data via RESTful resources, sockets and flexible plug-ins.

CloudBoost can power your app's backend, including data storage, user authentication, real-time notifications, search and more.

API development tool for Web and Mobile developers.

An open protocol for per-user storage

PubNub is the world’s only global Real-Time Network. PubNub enables software developers to rapidly build and scale real-time apps by providing the cloud infrastructure, connections and key building blocks for real-time interactivity. Developers can build real-time apps like live dashboards and data streams, real-time collaboration, 2nd screen synchronization and machine-to-machine signaling for any device. PubNub utilizes a Publish/Subscribe model for real-time data streaming and device signaling and supports all of the capabilities of WebSockets, Socket.IO, SignalIR, WebRTC Data Channel and other streaming protocols. With PubNub, developers can dramatically reduce the cost, complexity and time to deliver real-time experiences. »

Build your app in minutes. No vendor lock-in Deploy BaasBox anywhere you like with SDKs for iOS, Android and Javascript

Emitter is a real-time communication service for connecting online devices. Infrastructure and APIs for IoT, gaming, apps and real-time web. At its core, emitter.io is a distributed, scalable and fault-tolerant publish-subscribe messaging platform based on MQTT protocol and featuring message storage.

MongooseIM is aimed at large, complex enterprise level projects, where real-time communication is critical for business success. It provides high availability, ease of deployment, development and reliability in production.

Heroic Labs are the developers behind Nakama server - The open-source social and realtime server for apps and games. Nakama powers social friends, groups, in-app chat, leaderboards, storage, matchmaking, multiplayer and more in a single server binary.

A secure realtime server, supporting data-sync, RPCs and events