SPIP is a free content management system released under GNU/GPL license. The letter P in the word SPIP stands for French Partagé (shared) or Participatif (participative), it indicates that the main goal developers have in mind creating this CMS is the orientation towards collaborative editing.
SPIP is very easy and intuitive to use. As opposed to another content management systems which sometimes impose very rigid structure of the page, SPIP allows to create adjustable, magazine-like structure with sections, subsections and so on. The CMS allows to easily layout your articles using blend of HTML and its own mark-up language. All pages inside SPIP are generated on the fly, however caching system generates pre-made pages with user defined life-span to increase loading speed and to decrease server load.
If you really like the features that SPIP offers, you can effortlessly convert your website using CMS2CMS. Process is fully automated and does not require programming skills.