Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.

enduro.js - Code-only, no-clicking, flat-file, node.js cms for professionals. With everything needed - Sass, iconfont generator, spritesheet generator, templates...

Anchor CMS - Free and lightweight blogging system

KeystoneJS - Open source framework for developing database-driven websites, applications and APIs in Node.js.

Textpattern - Textpattern is an elegant content management system that is free, open source software.

HashBrown CMS - A truly different approach to content management. Instead of being on-site, HashBrown publishes content to your website remotely, so you can build them using whatever language or framework you prefer.