Calcoo

Calcoo is a scientific calculator designed to provide maximum usability. Its features bitmapped button labels and display digits to improve readability, no double-function buttons, undo/redo buttons, copy/paste interaction with the clipboard, both RPN and algebraic modes, two memory registers with displays, displays for Y, Z, and T registers, and tick marks to separate thousands. Calcoo is written in C using the GTK+ widget library (v.2.2+). (Source: http://freecode.com/)