Heard about Concrete5 in a podcast from twit.tv called Floss Weekly [ FLOSS Weekly 239 ]. Am currently using Podax on Android to retrieve and listen to my podcasts and gPodder on my desktop to manage the shows I want. That's a hole other topic though so let's get back to how awesome Concrete5 is, and how they have successfully utilized Open Source and Creative Commons as the basis for their business model.
Concrete5 is a content management system that is free and open source, made for marketing but built for geeks. Concrete5 was designed for ease of use, for users with minimum technical skill can still make beautiful pages. It enables users to edit site content directly from the page. It provides version management for every page, similar to wiki software, so any edits can be viewed and reverted back to, also allows users to edit images through an embedded editor on the page.