osCMall system is based off of osCommerce but extends the ability to be used by multiple vendors using 1 database and source code (similar idea to ebay stores).
A site which is using this software (very customized though) is www.mystore.com.
There are many small issues and testing needing to be done as, including to build a more comprehensive user manual.
Peter who is leading the project does offer some support through http://forum.systemsmanager.net/.
Students that whish to work on this project (be it 1. to identify (and fix) bugs, 2. to contribute to the code, or 3. to draft / improve the requirement specification documentation) , please contact Peter by mail at firstname.lastname@example.org