Open Source Commerce, and online store management and e-commerce software program. It is a self-hosted and open source program that can be used on any web server that has MySql and PHP installed. It can be downloaded for free under the GNU General Public Licence. Os Commerce helps you with setting up your online business, its marketing, and management. The latest Os Commerce development version is 3.0.
Pros
Easy to Customize according to user needs.
Can be extended easily
Offers Expert Support
Pretty great Templates
Popular and well established
Provides inbuilt features like Multi-Currency support, Statistics, etc
Cons
Self Hosted which means that you’ll need to deal with site maintenance, updates, hosting, etc all by yourself.
More prone to errors
Difficult to scale