Mycodo – open-source environmental regulation system

I set up an Arduino-based programmable logic controller to manage the fogging and primary heating circuits for our commercial greenhouse, with a separate Node.js-based server component that handles only Arduino configuration changes, logging and alerting and it works beautifully. The idea of having a full Linux machine (especially in a RPi form factor) running the process control functions would be a bit scary.

Still, the capabilities here seem so far beyond what you could do with a single PLC that it's very impressive and I can definitely imagine using it for something non-critical, or with multiple hardware backup systems.

edit: I am dumb and didn't scroll down far enough on the github page to see the pictures.