Pagehand allows you to group related font families together into a font category. Font categories exists only in Pagehand; font categories are not available to other applications.
Mac OS X includes a utility called Font Book that allows you to group related fonts together into a font collection. Font collections are available to any application that knows how to use them. The Pagehand font palette and the Apple Font Panel both work with font collections.
Font categories and font collections are very similar. You can use either, both, or neither. The main advantage of Pagehand font categories is they are already set up in a far more useful manner than Apple font collections.