Here's a link from early last year at LinuxLookup
that does a pretty good job at giving an overview of a few CMS's.
Here are the first things that come to my mind though:
-- Forked from phpNuke
due to author's choice of development style and practices. Postnuke has very nice security & functionality as well as a huge community for support, themes, modules, and blocks. Simple to setup.
-- a parallel of Postnuke with improved default security & cleaned up code.
-- Forked from Postnuke -- nice theming abilities beyond that of Postnuke due to the integrated Encompass engine based on Smarty.
-- Forked from Postnuke -- most of the core developers moved to this dev team last year. They just release .9beta a couple days ago.
-- Don't know much about this one. Similar to phpNuke/Postnuke I believe.
-- Don't know much about their software either.
is a python based one that seems a little more complicated to use & get running/customized.
The Nuke variants are the projects I currently follow. Personally, I use Envolution on new sites & have a couple Postnuke sites that I haven't converted yet.
I haven't played with Tiki yet, but I do know there is a phpWiki module available for the Nuke variants.