The mailing lists
From Rivendell Wiki
The Rivendell mailing list at groups.io is a good place to get help on Rivendell, with both developers and users maintaining an active presence there.
The Rivendell google groups at rivendell-dev (covering Mar 2007 to April 2012) and rivendell-programmer contain archives of the previous Rivendell mailing lists (covering Mar 2007 to September 2022.