Brewing occupies my weekends sometimes, but so does writing software.
BrewBench is a beer monitoring system that runs on an Arduino. It is a kettle temperature monitor, controller and notification system that can also work as a RIMS system. The app also can monitor temperatures on glycol, fermenters, walk-in coolers and anything else. Check it out on hackster and the code on github.
KettleTop is a contract pro brewing company using software to monitor and make better beer.