Asteroid Belt
Asteroid belts span a whole solar orbit with hundreds of small unstable tumbling rocks. They may contain one or more stable planetoid worlds, which can be landed on and colonized.
The unusable tumbling rocks in the belt have no collision and cannot be targeted or harvested. Presence in an asteroid belt will also increase the density of the small debris that indicate movement in space.
Planetoid
At first glace the planetoid are simply very small airless worlds with fast rotation. But they might have antiflux particles in their nonexistent atmosphere which can be exploited with a refinery.