Seth Gottlieb, Content Management Practice Lead of Optaros, recently published a white paper comparing 15 open source CMS offerings.
The stated goal was primarily to assess the utility of the resources (books, online documentation, and community/forum support) for a given CMS offering, but each assessment also contains a quick overview of the product and describes its basic use and a few architectural details. Seth puts the onus back on the consumer for the assessment of system fitness, stating quite reasonably that this depends greatly on the project requirements.
For those of you in the midst of a very time consuming CMS product assessment exercise, this report is worth getting your hands on.
Content Management Problems and Open Source Solutions