CometD

CometD is a scalable comet and WebSocket messaging library for web applications, providing publish/subscribe, RPC, and peer-to-peer communication patterns. The current stable version is 9.0.0, released under the Apache 2.0 license. It ships TypeScript types and supports ES modules. CometD replaces the older cometd-jQuery and provides a modern, promise-based API. It differentiates from alternatives like Socket.IO by being more lightweight and focusing on the Bayeux protocol with built-in support for long-polling, WebSocket, and extensions like time-stamping.