CKEditor - Real-time collaborative future-ready rich text editor
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
TinyMCE - TinyMCE is a content editor that functions as a plug-in for Wordpress websites.
Anchor CMS - Free and lightweight blogging system
Quill - Powerful, API-driven rich text editor
Textpattern - Textpattern is an elegant content management system that is free, open source software.