Node-RED is an open, development tool most often associated with Internet of Things (IoT). It is free and comes pre-installed on Raspberry computers.  It also operates on Unix, Windows and Mac.

See an on-line  running demonstration of  Node-red

Access the mysql database used by Node-red via Adminer

The Server :
The user     : admin
The password  : Michael34! 
The database : demonode

It has many features and a very active user community. Flows may look complex, but in actuality they built using simple tools selected from the palette and configured in the Flow window.   These are collaborative tools permitting developers from around the world to work together.