This is the Range Oscillator coded by Mladen and is very similar to the "raw" Stochastics and Williams Percent Range.
As explained by Mladen:
The Range Oscillator is an indicator that shows the relative position of median price in the highest high to lowest low range for desired period. It is bound to 0 - 100 range, hence those levels are the extreme levels. Usage should be similar to stochastic indicator.