Technologies in the Film
The iconic pink hoverboard plays an important role in Back to the Future II and actually saves Marty's life several times because of its versatility. Such technology does not exist today, and most likely will not exist by 2015 as the movie predicts given the state of research today.
Multiple attempts have been made to create some sort of hovering platform, but anti-gravity-type technology is still not possible today, despite this promotional video featuring Tony Hawk and Christopher Lloyd. Other methods, such as firing water or air jets at the ground have been attempted today, for example on MythBusters , but these are not yet viable technologies for creating hoverboards because of power consumption and sustainability issues.
Existing technologies today that hover to some degree include hovercrafts, which blow jets of air downward and force it to exit from underneath the craft, creating a cushion of air on which to ride on. They move by pushing air behind them using giant fans. Hovercrafts are robust because they are able to travel on grassy terrains, rocky terrains, plains, and even water, but are not suited for many situations because of the noise pollution caused by the fans, the powerful air gusts or water sprays which can knock bystanders over, and speed and maneuverability sacrifices, as best exemplified by Top Gear . The hoverboard in Back to the Future II, on the other hand, manages to accomplish the same versatility without the noise and jets of air and water and with better maneuverability.
The way the hoverboard is portrayed in the movie implies that it employs advanced computing to measure the weight distribution of the user, the force with which the user steps on each end, the speed at which it is traveling, and when the user is trying to move forward or keep it still. It is able to stabilize itself, vary the distance from the ground (or wall), absorb impacts with the ground before they happen, and apply enough pressure to keep itself from sinking too low. Many of these are similar to the abilities of the flying DeLorean. The computing involved in these processes is immense, so it will be some time before this type of computing power can be shrunken down enough to fit inside a board, as well.