Mosquitto is the reference open source MQTT broker, and it is small enough to run almost anywhere. A ZoomEye query for the application fingerprint records 1,160,264 matches. How the number was obtained The query was app="Mosquitto", run against the ZoomEye index on 29 September 2026 at 02:47 UTC.
Source: [Dev.to](https://dev.to/jeffreyciend/1160264-mosquitto-fingerprints-the-mqtt-broker-that-ends-up-on-the-public-internet-ni5)