No. 4: Sewage Pig
On one episode of TV's "Futurama," famed robot Bender "Bending" Rodriguez noticed a small robot cleaning up some trash. Outraged, the feisty automaton exclaimed, "And look who's cleaning up the crap! A human child? I wish!"
Bender would likely express even more outrage if he were to travel to modern day Germany, where electric mole or "pig" robots are, quite literally, cleaning up the crap. Produced by Thermo-System, the wheeled robots truck through human waste, using harnessed solar energy to help dry an estimated 60 millions tons (54 million metric tons) of sewage a year in Germany alone [source: Thomas]. As the robots truck through the sludge, they also turn it, aerating the ravenous microbes.
Robot civil rights issues aside, the electric moles keep operating costs and carbon emissions low for sewage treatment plants.