Rola-bola

The rola bola (also known as a "rolla bolla," a "rolo bolo," a "roly boly," a "balance board," a "rocker-roller board" and a "bongo board") in its simplest form is a plank on a cylinder on which a person balances. The plank rocks back and forth on the cylinder like a seesaw but its pivot point shifts back and forth as the cylinder rolls beneath the plank. With a bit of practice, balancing on a rola bola is not too difficult.
Source: http://en.wikipedia.org