These are a series of Tech Tests, demonstrating best practices in Test Driven Development, Object Oriented Design principles, and Agile/XP methods.
In summary, the program allows you to create an account, deposit funds into it, withdraw funds from it, and print statements.
I completed four separate implementations, in three languages, over the course of a week.
Implementations are in Ruby, JavaScript for the browser, Node.js, and Python.
The specific requirements, instructions, and full documentation of the development process is available in the READMEs of these projects.