The most common variation of the ollie is the nollie (short for "nose ollie"), where the rider reverses the roles of the two legs so that the front foot pops the nose to the ground, and the rear foot lifts and guides the tail.
The switch stance ollie uses a similar body motion, but the nollie is subtly distinct: For one, the rider is always moving forward, with the body positioned in a nollie stance--closer to the nose and with the front foot on the nose. Secondly the rider usually postures the body differently to compensate for this stance with respect to the forward motion.
Read more about this topic: Ollie (skateboarding)