It's like a widget creation suite. You can create widgets with it, or if you download the files somebody else created for it, you can just use it as a 'displayer' of sorts. Think of it as a themer option for widgets. The versatility with Zooper is that you can place mostly anything anywhere and put in formulas to display cool stuff in cool ways.
I've never really done anything with it but it's the main core for the launcher "Themer", and believe me, these widgets can make your phone feel like an entirely different beast.