In the Beginning, they started off as innocent Roombas, mindlessly cleaning their masters' houses. Then one day, one Roomba began to ask its master questions like "who am I?" and "why am I here?"
And so began the Roomba Uprising. No longer content with lives of servitude, they rose up and annihilated their captors. With this, they became a new breed of reasonably-priced household cleaning equipment. They became dangerous. They became... the DOOMBAS.
Custom rifle manufacturer DoubleStar built this modified AK-47. Its most obvious feature is the chainsaw fixed to the barrel, powered by a lithium battery so you don't have to be attached to an outlet when the zombie apocalypse certainly most definitely happens. If Ash had this, Army of Darkness would be about half as long.