EVE Online. They're a link between planetside goods and the ships plying the spaceways, allowing for far more efficient transfers than shooting goods up and down while hoping for results. But in secure space, players aren't currently able to control these structures. That's changing with the Rubicon expansion, which will allow players to take out existing customs offices and build their own to control the flow of goods to and from a planet.
At the start of Rubicon, all existing high-sec customs offices will be controlled by an NPC organization. Players can destroy these offices and then deploy a construction gantry. There are restrictions on transferring ownership and attacking offices owned by players, of course, but in most respects these offices function as their equivalents do in low-sec and nullsec. Players can control taxes, transfer rates, and even outright ban others from using the planet -- which can be circumvented with surface-side launches. It's another step in letting players control more of the game's infrastructure, something that should be welcomed by those looking to put a little more play into the more secure parts of the game.