... I call it the soccer ball slider ;)
The idea was to make an interface for browsing linear content that was minimal (in terms of controls) but fun, unique and which also allowed subtle control.
It's mostly just useful as an alternative to a regular scrollbar, but it can also be used as a "playhead" by rolling the ball in a certain direction at the speed you want to view the content. Or you can "shuffle" by kicking the ball randomly.