An easy to use, flexible way to manage a Web site. It has requirements other than what comes with OS X. It's not meant for someone who doesn't want to do any work though as you need to write your own template (requires HTML knowledge) and static pages are written using PHP syntax. Although if you use the WIKI features you can write your pages using a rich text editor (not Safari compatible yet.)
The whole idea of MachCMS is to make managing a Web site easy without the need for complex modules or plugins. It uses a page based system.