concrete5 is an open source content management and website builder application.
Building and running a website are two very different challenges. Certainly, one person may wear both hats, but the process of launching a great website is far different from running a great website over time. concrete5 lets you do both: build and run great websites. Most other content management systems are built for one side of the equation or the other.
Many CMS's were designed by developers, for developers. Building and maintaining a site with them can be pretty complex and intimidating for someone who can't program computers. The end editing experience works, but to make even basic content changes you're typically working with long web forms in a "back-end." Adding new functionality is something you'll need some technical know-how to pull off. Imagine having to call a consultant every time you wanted to write a new Word document. How useful is that to your business?
Conversely, there's a number of solutions that are geared for the DIY market. Typically starting as a blog, these sites get added to and added to over time until they fall apart. Imagine being told your document was always going to have a cover page, a table of contents, and an index – no matter how simple you wanted it to be. Sure it's great you can get started quickly, but if you want to do much more than what these systems were designed for like using a hammer to drive screws.
With concrete5, you get the best of both worlds. Anyone can start making their own website in seconds, and the editing experience is easy; just click on what you want to change. Developers still get a flexible and robust framework for building sophisticated web applications. With concrete5, however, site owners will be able to make changes and additions on their own, for years to come.