CheckbooX is a Mac OS X application that mimics the register included with your checkbook. It comes complete with source code. It's the application I used as an example in my article Unit Testing with OCUnit, published on O'Reilly's MacDevCenter on April 23, 2004.
Since I've just released CheckbooX for the first time, there's not much more to say. Please see the file CheckbooX Readme.rtf; it is also included with the application.
Download CheckbooX (150K, including source).
CheckbooX is Copyright © 2004 by Jim Menard. It is copyrighted free software released under the Apache Software License, Version 2.0, a copy of which may be found at http://www.apache.org/LICENSE.txt.