For the homebrew hardware nerds out there who also homebrew beer: "BrewPi is an open source fermentation controller that runs on an Arduino (for now) and a Raspberry Pi. It can control your beer temperature with 0.1 degree precision, log temperature data in nice graphs and is fully configurable from a web interface." Source code. The article has lots of photos and screenshots. The project involves rewiring the compressor's electrical connection through a PID controller, and includes both a fancy OLED display on the fridge and support for logging statistics and control over the web. If you've ever had the joy of gradually crash-cooling a lager (not too fast, not too slow), the software includes settings to effect gradual temperatures changes in the fermenting wort. Certainly fancier than a Johnson controller and a probe attached to a fermenter with a strip of insulating tape.