Skyhooks

Skyhooks are massive momentum exchange tethers that reduces the cost of placing payloads into low Earth orbit. Aircraft can dock with the lower end of the cable in its slower Orbit and then ride along the cable to the other end of the cable out in Space.
They are positioned only at strategic locations where cities need cheap travel of aircrafts to space stations in low Orbit, but they are only capable of transporting small aircrafts, as opposed to larger ships using a @Mass Driver

Utility

Rotating Skyhooks caller Rotovators can slow down and pick up objecta even closer to the ground and have been used to pick up Cargo on high altitude locations to scoop things right off the ground into orbit.

Discovery

Until the widespread use of carbon nanotubes and graphene there were no materials strong enough to hold the tethers together.