Three is a daily application for doing trivial calculations using the rule of three!
If my car consumes an average 8.8 litres of gas per 100 kilometers, a 350 kilometer trip will consume 30.8 litres (and therefore $61.6 if gas price is $2/litre)…
…or a fast currency converter: if 1 Euro is about 1.11 US dollars, 33.9 EUR is 37.63 USD.
Three can also be used for coordinate measurements, image resize, even grocery shopping.
As simple and trivial it is, the rule is used every day in simple daily arithmetics.
The application has a simple and modern interface to perform fast calculations and includes some basic options to facilitate the display results (thousands separator, number of decimals)
It also includes a result spell out for another flavor!