There are at least six different traditions of the Six-armed Mahakala (shadbhuja). The most famous and well-known is produced more as art. It is called Shangpa Kagyu tradition Mahakala.
The Six-Armed Mahakala is the ferocious form of the Bodhisattva Avalokiteshvara. In the painting, Mahakala is seen furious with six hands holding his horrific ritual implements.