Ruby on Rails App - Google Wallet and PayPal Feature combined with mobile payment.
Create/Delete/Edit user functionality
Admin user accounts with special privileges
Grant credit card access to others
Ability to send/receive funds
Form validation checking (making sure forms are submitted securely, valid telephone number format submitted, valid password length, etc)
REGEX Card Algorithm to figure out which type of credit card type has been entered (Visa, MasterCard, etc) and to make sure it is a valid card number