Windows 7 Enhanced Calculator

Windows' built-in calculator hasn't really changed much over the years, but Windows 7's calculator has a few extra tricks up its sleeve, which you'll find in the 'View' menu. It can do myriad kinds of unit conversion (temperature, weight, area, and others), interesting date calculations, and even has worksheets to calculate a mortgage payment or a car's fuel mileage. It also maintains a history of your previous calculations as long as the program is open.