At the push of a button this spreadsheet automatically randomly generates new worksheets (and an updated key) for what we call "mad minutes."
Mad minutes consists of 20 arithmetic problems that students are to complete at a relatively quick pace without a calculator. The purpose is to increase numeracy and automaticity. I've even used these in Calculus to enhance students' number sense.
I can add other worksheets/functionality if requested and I will release updates free of charge.