Cloudflare has announced the private beta of its programmable message bus, Cloudflare Pub/Sub, built on the widely-used MQTT protocol. The service allows developers to publish event data from any MQTT-capable client and write code that can filter, aggregate, or modify messages before they are distributed to subscribers. It also enables pushing events from applications in other clouds or on-premise, with Pub/Sub acting as a programmable event router or a hook into persistent data storage like R2 or KV. The beta aims to support the MQTT v5.0 specification and provide an accessible free tier for developers.