[Madlug] Content Management Systems

[Robert Norton]

Hello,
My son started www.flakmag.com and has been working on it for a long
time.  He would like to make it easier for himself and the other authors
to post their articles, so he asked me to look into CMS programs.  Of
course I know nothing about this yet, so I am wondering if somebody here
can point me in the right direction.  

I've looked a bit at plone, Expression Engine, CMSmadeSimple, and
WordPress.  The program needs to run on Windows and Mac, and of course I
would prefer it run on Linux as well.  It has to be easy to use once set
up, as the authors may not be primarily technical folks.  

I would appreciate any experiences or rumors you may have had about
these programs, or other programs or ways of doing the job easily.

Thanks!