Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
WordPress - WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
Ghost - Ghost is a fully open source, adaptable platform for building and running a modern online publication. We power blogs, magazines and journalists from Zappos to Sky News.
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
Craft CMS - Content management system built on Yii PHP Framework