Drupal

 Drupal  is a popular open source content management system with excellent plugins for IndieWeb use.

Configure IndieWeb Drupal module
Ravi Sagar created a relatively short YouTube video walk through of the IndieWeb Drupal Module:
 * How to configure IndieWeb Drupal module?
 * https://www.youtube.com/watch?v=Z3tZXkhsiWU

How to Markup Drupal for IndieWeb
See Benjamin Melançon’s excellent step by step article:
 * Marking up Drupal's blog posts for the IndieWeb

Benjamin Melançon
Benjamin Melançon's site agaric.com uses Drupal and supports key IndieWeb markup building blocks for IndieAuth (rel=me), authorship (h-card), and readers (h-entry) since at least 2015-11-11.

Dries Buytaert
Dries Buytaert, the creator of Drupal, has been self dogfooding on https://dri.es/ since ????-??. He's been exploring POSSE and other related building blocks:
 * To PESOS or POSSE?

Kristof De Jaeger
's personal site https://realize.be/ is built on Drupal. From the humble start of supporting webmentions with webmentions.io integration, Kristof (also known as swentel) has been putting almost all of the building blocks into the impressive and still improving IndieWeb integration module for Drupal 8. (More about it in the Tools section below.)

Ravi Sagar
Ravi Sagar Drupal 8 site is using the Indieweb module for notes, checkins, replies, likes and issues. Content posting and social interactions are done through the site's interface, Indigenous mobile app and Monocle. Site is using brid.gy to syndicate content to Twitter and Github, responses are sent back to the site and displayed on the individual nodes.

IndieWeb Tools
Current module(s)
 * IndieWeb module for Drupal 8 - exposes webmention, micropub, microsub and indieauth endpoints. Adds microformats to your content and feeds. Webmentions can be send and various blocks are available to expose received webmentions, RSVP's .. Users can authenticate with their domain too. Release candidates right now, first stable expected february 2019. (see also article below by Kristof De Jaeger)
 * Linkback - Drupal 8 module with support for Webmention, Pingback, Trackback and Refback
 * 2017-12-04 released the alpha version of the Linkback module for Drupal 8.

Past module(s) (maintenance state unknown, much functionality superseded by above current modules)
 * Multiping – module that enables pinging a Pubsubhubbub hub when HTML or RSS feeds are updated
 * Vinculum – Drupal 7 module that enables both sending and receiving Webmentions
 * Micropub plugin for Drupal was begun on 2018-01-25 as a beta version, but likely isn't ready for production use yet.

Sessions
Sessions about Drupal at IndieWebCamps:
 * 2016-03-14 2016/MIT/drupal
 * 2015-03-19 2015/Cambridge/drupal - drupal discussion at IWC Cambridge
 * 2014-10-11 2014/Cambridge 2014-10-11 (Drupal introduced; no notes)