Node-RED

Node-RED, born at IBM and now an OpenJS Foundation project, lets you wire hardware, MQTT topics, HTTP endpoints and services together by dragging nodes onto a canvas. It is a fixture of the IoT world and runs comfortably on a Raspberry Pi.

Flows are quick to build and easy to understand at small scale; very large flow collections can become their own maintenance burden, so name and organize things early. The community node library covers almost any device or protocol you can think of.

Ideal for event-driven tinkering — the moment a sensor reading should turn into an MQTT message and a notification, Node-RED is the shortest path.