osCommerce is a versatile shopping cart script used by hundreds of websites. As a shopping cart script with numerous pre-built functions, plugins ( or user generated contributions) it is undoubtedly comprehensive. However , just to exemplify, some of the key features include :

• web based install
• supports unlimited products and categories
• includes options for physical goods and e-products
• includes taxation as an option
• accounting and invoicing
• customers and transaction reports
• newsletter subscription module
• product reviews
• banner management and statistics
• payment processing using several credit card and web payment options

and many many more .
In my opinion, it has too many options to be able to be listed , even though some of those functions or options might not be necessary for a website owner who requires a shopping cart system for his website. Now, not all of these are advantageous to a basic website operator / owner , and he may even be bit overwhelmed seeing so many options , and requiring to ensure that the ones which are not required are turned off / disabled. As the service provider / web developer / programmer , we often have to ensure that most of these options are turned off or in cases which can not be turned off from the Admin panel, are removed from the php files .
One of our recent osCommerce projects involved several customizations on the base script - one part of which was ensuring around 40-45% of the default osCommerce features be removed from being available in the admin panel , based on instructions given by our client. One of the major customizations we also did was , by default osCommerce allows one cart / shop inside it , but in this case the requirement was to setup 2 separate carts and ensuring that they be administered from one single admin panel. Now this is not a default feature , nor is any proper contribution could be found for this. So it had to be programmed totally from new. The end result was undoubtedly quite nice , as we gained quite a bit of experience in doing this. The end users / visitors to the site would login to the website and find a wine shop as well as a news and magazines shop and wherever they went or registered, they had to login only once and also on check out or buying, the admin would be able to track the customers or the orders from inside the same panel only.
below are screenshots .
Cart 1 and Cart 2.