SpeedCrunch is a multiplatform desktop high-precision scientific calculator
for power users.  It is designed to be enjoyed using keyboard.  Results are
shown in a syntax-highlighted scrollable display, history of expressions is
available with up and down arrows.

Some other features: optional keypad, matching parenthesis indicator, auto-
completion of functions and variables, just-in-time calculation (show result
while still typing), a formula book, and quick insertion of constants from
various fields of knowledge.

WWW: http://speedcrunch.org/