Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
WP Rocket - WP Rocket offers a caching plugin for Wordpress.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
Yoast - Yoast offers plugins to improve SEO and optimize web sites and blogs.
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
Wordfence - Comprehensive security plugin for WordPress.