As the name implies, this is one of the simplest CMS systems around.
I've searched for a simple CMS solution for my customers and couldn't find one, so I decided to write one myself!
This version has the shopping cart integrated into the CMS.
deCMSOrder isn't open source, but it's very reasonably priced.
For $2,500 AUD you can have your site up and running in no time at all and this covers the 1st year's web and email hosting too!
I've also written a dynamic version of this system, eInfoCMS, which is very similar, plus an additional module for a simple shopping cart/ecommerce solution, eOrderCMS. For $2,500 AUD you can have a complete shopping solution which is dead easy to maintain.
deCMSOrder covers it all:
Some of the shopping cart features are: