Long ago a great empire spanned the stars until it collapsed. The worlds of this empire fell into an intergalactic dark age and forgot their past. In the Aldus solar system, spaceflight has been regained. Two different races, the Malus and the Alyssians, both venture out into space for the first time and encounter one another. Due to fragmented legends among both races, they soon grow distrustful of one another and declare war. However the Alyssians and Malus are weak in resources, having been confined to their planets for so long, and so it's important for both sides to establish Offworld Resource Bases.

O.R.B. is a 3D real-time strategy game, similar in gameplay to Homeworld. The player must build up bases and oversee the collection of resources in space. These can then be used to construct new vessels and spaceships as well as research additional abilities. Asteroids and planets can provide a strategic advantage in the positioning of forces. The player can assign movement and combat orders to individual units or as a group.