Ranco ETC (Electronic Temperature Controller) model 111000.  Use as an overriding thermostat to control your kegerator deep freeze or refrigerator or fermentation chamber.  Single stage digital temperature controller.

Update: Since this post was published the price, availability or promotion has changed.  Check the product page for current description, price and availability.  Also: Today’s Deals on Amazon

RANCO ETC-111000 Digital Cold Temperature Control NEW

Also Consider: Inkbird Dual Stage Temp Controller

Resource Pages: Yeast Starters & Fermentation | Kegerator Tips & Gear

More: Recent Amazon Finds

Inkbird ITC-308 – Dual Stage Digital Temperature Controller