While vaguely humanoid, the Mark I assault droids relied on a single leg for movement. They were capable defenders, but had little in the way of advanced tactical programming. It carried one blaster on each arm for a total of two and was not above clubbing people with its arms at close quarters either. They also occasionally had a shield which generated a bubble of energy capable for absorbing blaster bolts and lightsaber strikes for short times.
Mark I assault droid was originally created by Galactic Republic in the days prior to the Mandalorian Wars, but later became one of the most common droids in the Sith Empire. While the Republic put them as automated defenses on patrolling cities or military installations, the Sith Empire used these droids to fill out their military ranks and also as defense forces on the starships throughout the fleet. These droids were used primarily in a defensive manner and, despite their simple programming, proved exceptionally capable of repelling Republic boarding parties attempting to seize Sith starships.
At one point in Knights of the Old Republic, this model is referred to as assault droid Mark II, but this was probably a typo. It should not therefore be confused with the quadrupedal model of that name.