I've the following points about these three open source carts..
osCommerce Cart : osCommerce or Open Source Ecommerce is an free e-commerce and online store-management software program, which can be used on any web server that has PHP and MySQL installed.
Zen Cart : Zencart is also a free online store management software program launches recently. It is also based upon PHP, MySql and HTML components. It supports numerous languages and currencies.
Cube Cart : Cube cart is the ecommerce shopping cart software solution that is launches in 21st April 2010. It is also a free ecommerce shopping cart software solution that can easily create a powerful online store.