Is that an immersion water heater circulator?
I've seen some Maker articles on building your own that I've want to try, they look pretty neat. You use them to dial in water to a very specific heat, most famously to make ridiculous poached eggs (pictured)
You can do other things, like cook a vacuum packed steak to medium rare all the way through, then just slap it under a heat gun or blow torch to sear a perfect steak. You can even use it to warm up avocados to a temperature where their browning enzymes break down, for guac that never turns dark on you.