SpeedCrunch

SpeedCrunch is a fast, high precision and powerful desktop calculator.
Available for Linux Linux, Windows Microsoft Windows, and Mac OS X.

Few of its distinctive features are:

scrollable display
up to 50 decimal precisions
unlimited variable storage
intelligent automatic completion
full keyboard-friendly
more than 50 built-in math function
optional keypad

And enjoy also the convenience featurelets:

on-the-fly calculation
customizable appearance
syntax highlight, with parentheses matching

Learn more or download it now. It's completely FREE!