The Arduino and Cloud-based homebrewing controller by Martin Kennedy of TheBedroomLaboratory:
It’s just a basic site, based on this Scotch.io tutorial, which is currently plotting the temperature in my sitting room. It’s got a PHP backend (Laravel framework with RESTful API), MySQL database and an AngularJS frontend with (n3-chart/d3 for the graph). In the house, I’ve whacked together a quick breadboard circuit which comprises of an Arduino clone, a DS18B20 Temperature Sensor (with resistor for the i2c connection) and an ESP8266 module. Every minute, this wireless sensor POSTs the temperature to our REST API. This value is saved in the database and will appear in the graph whenever the page is opened. To hook it up to a fermenter, the sensor would just be placed in a thermowell in the fermenter bucket so we can see the beer temperature over time.
The design files is available on GitHub.