Tiny, Hackable Quadcopter Drone Launches Pre-Orders
As these get smaller and smaller, we get closer and closer to a dog pod grid:  Aerostat meant anything that hung in the air. This was an easy trick to pull off
  nowadays. Nanotech materials were stronger. Computers were infinitesimal. Power
  supplies were much more potent. It was almost difficult not to build things 
  that were lighter than air. . . .

  Given that it was so easy to make things that would float in air, it was not 
  much of a stretch to add an air turbine. This was nothing more than a small 
  propeller, or series of them, mounted in a tubular foramen wrought through 
  the body of the aerostat, drawing in air at one end and forcing it out the other
  to generate thrust. A device built with several thrusters pointed along 
  different axes could remain in one position, or indeed navigate through space.

  Each aerostat in the dog pod grid was a mirror-surfaced, aerodynamic teardrop 
  just wide enough, at its widest part, to have contained a pingpong ball. These 
  pods were programmed to hang in space in a hexagonal grid pattern, about ten 
  centimeters apart near the ground (close enough to stop a dog but not a cat, 
  hence "dog pods") and spaced wider as they got higher. In this fashion a hemi-
  spherical dome was limned around the sacrosanct airspace of the New Atlantis 
  Clave. When wind gusted, the pods all swung into it like weathervanes, and the 
  grid deformed for a bit as the pods were shoved around; but all of them even-
  tually worked their way back into place, swimming upstream like minnows, pro-
  pelling the air turbines. The 'bines made a thin hissing noise, like a razor 
  blade cutting air, that, when multiplied by the number of pods within earshot, 
  engendered a not altogether cheerful ambience. Enough wrestling with the wind, 
  and a pod's battery would run down. Then it would swim over and nuzzle its 
  neighbor. The two would mate in midair, like dragonflies, and the weaker would 
  take power from the stronger. The system included larger aerostats called nurse 
  drones that would cruise around dumping large amounts of power into randomly 
  selected pods all over the grid, which would then distribute it to their neigh-
  bors. If a pod thought it was having mechanical trouble, it would send out a 
  message, and a fresh pod would fly out from the Royal Security installation be-
  neath Source Victoria and relieve it so that it could fly home to be decompiled.

--Neal Stephenson, The Diamond Age