SimpleCalculator is the best alternative for a slim and easy to use computer calculator. It works exactly like the normal pocket calculator you already use every day. It is very slim so it is easy to use and with its "Always on top" feature it will always be in sight while working in another application.
You can do all the basics mathematics operations with exponent and percents. You can easily calculate taxes with the percent function that will add the percentage to the original number if you enter your number, then press + and enter ur percentage. You can also copy any result and paste it anywhere you like, or copy a large number and paste it in the calculator.