The Sentient Furnace is one of the two Bosses in the Factory Dungeon. It was one of the machines that achieved sentience and was able to rebel against the humans. It awards the achievement 'Getting Even With the Oven' upon defeating.
Sentient Furnace: YOU ARE NOT READY!
Sentient Furnace: OH... BURN.
This is still available only in Beta since March 1st, 2014.