I'm looking for a good, easy to use and manage, free Content Management System that is built for (or can handle) multiple sub websites, or groups. Something like Drupal's Organic Groups functionality, except I don't want Drupal. My goal is to create a main site mydomain.com that sells websites (for guilds) at guildname.mydomain.com.
Thanks to Alerty for recommending the SilverStripe CMS, which works great! Although I've marked this as answered, if anybody else knows of any other ones, that would be great to know to.
EDIT: preferably something that won't requite multiple installs? I want any subscriber to the main site to be able to just pay $n and then click a "start site" button, which would automatically set up a new group/sub-site.