Can you be more specific, do you have an e-commerce product in mind?
You can use web scripts to mashup content into other applications, you can read more here, http://wiki.alfresco.com/wiki/Web_Scripts. Basically, you can write a url-addressable script to access content or content services. That is one way and probably the simplest way to approach integration. There is also a Java foundation API that provides full access to the repository. You can read more about the standard interfaces here, http://wiki.alfresco.com/wiki/Architecture.
