TYPO3

 TYPO3  is a large content management system written in PHP.

Plugins

 * IndieWeb Publishing Tools extension adds webmention support.
 * Maintained by Joschi Kuphal

IndieWeb Examples
IndieWeb community members running TYPO3 on their primary personal domain:

Joschi Kuphal

 * Joschi Kuphal uses TYPO3 on https://jkphl.is/ and maintains an indieweb extension for it: