The Unicyclopedia/BC wheel
The BC wheel (or Impossible Wheel) is a single wheel with pegs or small platforms connected to the axle. To ride you must balance on the pegs as the wheel is rolling. The name comes from the popular comic, B.C. by Johnny Hart, in which the characters travel by rolling on large stone wheels.
Riding the BC requires some different skills to the unicycle or Ultimate Wheel since fine control of the wheel's rotation is not possible. Since it requires very good balance it is not recommended for beginners. Advanced riders are able to do many tricks, including a variety of mounts, backwards riding, jumps and grinds.
The reason I love to BC so much is this: the most fun I've ever had on a uni was when I first got one, and just learning to ride those first few days. I fell so much but I was progressing I never had a balance point it was always hit or miss, and I get that everyday with the BC wheel. There is never a balance point you can get down to minimal movement but your still focused solid on what you're doing.
Protective Gear 
A very thick, strong, flexible, and heat resistant wrap or strap-on guard is important for braking and control. Gloves are recommended since, in some falls, you will hit the ground hands first. A skate-type helmet that protects the back of your neck is also recommended in case you fall backwards.
Freemount: This is similar to the freemount for an ultimate wheel. Whilst standing still, place one foot on a plate and angle the wheel away from that leg. Angling the wheel prevents it from touching the leg when pressure is applied to the footplate. Roll the wheel forward and kick off from the ground with the other foot; this supplies the initial momentum for riding the wheel. The second foot must then be placed quickly onto the other plate to maintain the balance of the wheel.
In this video Leo Vandewoestijne shows the Freemount
Roll mount: The wheel must be rolled along the ground in a straight line, which requires some skill in itself. The rider jogs up behind the wheel until they are close enough to jump onto the footplates. At the point of jumping, the rider should be careful to be running at the same speed as the wheel or it will be very hard to land correctly. On landing, both feet should contact the plates at (as near as possible) the same time.
In this video Max shows the Roll Mount
Skate Mount This is a relatively easy skill. The rider puts one foot on a peg or plate and pushes like one would push a skateboard, then puts the other foot on the other plate and rides away. This mount requires some dexterity and skill with the wheel to keep the wheel from rubbing your leg and slowing down when you have your one foot on the plate/peg.
In this video Evan Byrne shows the Skate Mount