It's a PHP class wrapper for handling WordPress Settings API. Gives a very handy way to build theme or plugins option panel.
A nice tutorial is presented can be found here about how to use this PHP class
It's mainly a plugin that demonstrates the Settings API PHP class
A plugin or theme developer can build their options panel with Settings API easily
Settings API is a functionality from WordPress that helps developers to save their options data very easily and securely. More about Settings API.