I was recently thinking about this: let’s say you built a chrome extension and wants to collect some basic usage analytics (with explicit user consent and knowledge, while preserving privacy) - you could batch-send activities at intervals to a REST-style API, but would be nicer to handle as a stream (eg to respond in real-time somehow).
Something lightweight like MQTT is also well suited for this. It was originally designed for telemetry messages in IoT situations but it also supports websockets so it can be used in web applications or browser extensions.
