What does X-Bc?
It basicly executes bc with some extra files that provide lots of functionality (trigonometry, number-theory, exponential functions, scientific constants, primenumbers etc.).
The input stays visible at all time so you can easily edit and reuse it using the mouse or emacs shortcuts to cut and paste.
Features:
"usual" scientific calculator functions
arbitrary precision
base conversions (e.g. hex → bin)
number theory functions
adjustable interface
In spite of all of these possibilities of scientific computing, X-Bc’s surface is held very simple and small, so that it won’t disturb on the desktop and will be easy to use, even for non-scientists (proven!).

License: GNU GPL.
Tags: arithmetic, arbitrary precision, calculator.
Interface: X.
Source language: C++.
Requires bc, GTK--.
Developer: Steffen Brinkmann.
Homepage: http://x-bc.sourceforge.net/.
Source repository: https://sourceforge.net/cvs/?group_id=64340.