Socket.io - Realtime application framework (Node.JS server)
Apache Tomcat - An open source software implementation of the Java Servlet and JavaServer Pages technologies
Ably - Serious realtime infrastructure
Glassfish - GlassFish v3, built by the GlassFish community, is the first compatible implementation of the Java...
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Payara Server - Payara Server is a fully supported, developer-friendly, open source application server. Innovative, cloud-native, optimized for production deployments. Jakarta EE & MicroProfile compatible.