Onewheel

 Unicycles or Monowheels or Self-balancing Scooters
   I have seen some gents lately, gliding quietly by, standing erect on one wheel and going very fast. Recently one passed me very quickly as I was going about 32km (20mph) on my ebike. I wondered what it was called and how fast it could go. 
   The answer to the first question is obvious and it seems as though "onewheel" is now the most popular term used to describe what is pictured below, but which also sometimes looks like a skateboard with just one big wheel in the middle. It can go very fast, as you will see if you look closely at the specs in the image. If you can't read it, this one can reach 140km (87mph) and I found another that costs closer to $6,000. This is a serious activity

   I also wondered what happened if you happened to come off of such a contraption at say only 30km, since it seemed to me that, even if you landed on your feet you would have to move them very quickly to stay on them. The person on the onewheel floating by me appeared to maintain his balance easily, but I also remember the Segway which had two wheels and people, including a President of the United States, often fell off them.  Apparently the younger generation is better-balanced than the older one since you will see in the video below a fellow riding on a trail on which many of us would be reluctant to walk.

Sources: 
   Wikipedia has all the information you will need, found conveniently under the term, "Onewheel." 
   You are more likely wondering, "What Ever Happened to the Segway?" since it was supposed to be a more important invention than the Internet. See Wikipedia again. It you are curious about who else fell, see: "Segway Ends Production of its Namesake After Two Decades of High-Profile Falls."
   Is it dangerous?  Of course: "CPSC Warns Consumers to Stop Using Onewheel Self-Balancing Electric Skateboards Due to Ejection Hazard: At Least Four Deaths and Multiple Injuries Reported."

  Do you think this fellow cares? No. Watch this INMOTION Adventure video which takes less than two minutes.