iConvert

iConvert is a dashboard widget that lets you work with more than 100 units of measurement to perform conversions. All of this with its free version. Specifically, there are 113 and they belong to the following categories: length, weight, data, volume, area, angles, time, data, power, pressure and temperature. For only 0.99€ you can purchase the 'pro' version of the widget which includes more than 500 units of measurement and new categories, including shoes, clothing or energy.