Free, it is mostly running for Swifitch project, but you can use it too for testing your IoT or whatever ;), it is running on Raspberry Pi profesional VPS.
field
value
address
broker.bevywise.com
port
1883 (TCP), 8443 (WebSockets)
type
Bevywise
info
web page. Secure. Need to sign up to view your devices. Use MQTT Authentication in your devices to connect securely. Free trial with unsecure ports (see https://devicemanager.bevywise.com/help)
field
value
address
mqtt.fluux.io
port
1883 (TCP), 8883 (TLS)
type
ejabberd
info
Free – no registration required, MQTT 5.0 compliant