Branch Space is a Traveller-esque space campaign set.

The core idea is that space systems are arrange in clusters that are traversable by shipboard faster than light drives, but movement between clusters can only be achieved through large gateway which. Thus the map of system clusters forms a tree like pattern, with the Trunk being the most stable and safe system (or those which appear to be so) while the distant Branch systems are far more exotic and unstable.

Branch Space