PG Calculator is a powerful scientific skinnable calculator.  It works in
algebraic and RPN mode, recognizes real and complex numbers, and allows
simple vectors manipulations.  It has up to 80 built-in functions, allows
user-defined variables, supports numbers inputing in binary, octal,
hexadecimal, and exponential formats.  Graphical user interface can be
easy changed with skins.

WWW: http://www.pgcalc.net/