Plone description
Plone is the leader in Open Source Content Management Systems (CMS), but brobably is better than most of the commercial offers out there, since it puts knowledge and power to build web sites and communities on the web in the ahnds of even the least skilled people
The programming language is Python, and there are many extensions to enable even more than the base capabilities.
One of the big problems is that all the extensions are not reviewed by users, but I think that the "rate" feature which is present on the plone site can be useful in this sense (the 2 "likes" or "dislikes" hands present in many pages or aside every product)