Lots of factors go into choosing an open source content management system: ease-of-use, compatibility with existing systems, support options, user communities, functionality. And while you don't want the selection process to turn into a popularity contest, knowing what systems are building critical mass and increasing (or decreasing) in popularity can be helpful.Water & Stone, an open source content management Web consultancy, has just released "The 2008 Open Source CMS Market Share Report" and the results are certainly interesting. Not surprisingly, WordPress is firmly in the lead, with Joomla! and Drupal in the second and third spots. The author, Ric Shreves, arrives at these numbers using a number of factors.

The report looks at 19 different open source content management systems, which it defines broadly as wiki and blogging platforms to more traditional CMS platforms. This breadth makes it a little tough to make apples to apples comparisons, but it's helpful data nonetheless.

In assessing the popularity and market share of the systems, the report looks primarily at downloads, installations, and third-party support, but also considers the number of books written on each of the systems, the relative popularity of their Web sites, volume of blog postings, ratings on sites such as OpenSourceCMS.com, and other data points.

It's fascinating to see how telling these factors are in highlighting the popularity and mind share of some up and coming platforms (Xoops, Typo3, e107), while also noting the tapering off of support and interest in other platforms (CMSMadeSimple, phpWebSite). And while popularity doesn't always equal quality and some small projects have incredibly dedicated volunteer support, these results are definitely something to consider when you're looking for a platform with longevity and the backing of a strong user community.

You can download a free PDF copy of the report from the Water & Stone web site. It's a good, insightful read, with a sound research approach and multiple charts and graphs to back up his assessment of various systems. I'd recommend that anyone currently in the evaluation process of open source content management system take a look.