The forum https://forum.openpetra.org has many years of history, it first was a phpBB forum, and then we moved to Discourse in 2014, and in January 2018 there was the migration to Flarum!
See my blog post from back then: https://www.pokorra.de/2018/10/migrating-a-forum-from-discourse-to-flarum/
We are using the Post Notification extension, see https://discuss.flarum.org/d/20750-post-notifications-per-e-mail
Over the years there has been lots of discussion on that forum, over the past years it has gone quiet again, for various reasons. But we are glad to work with Flarum, and it will help build a community for the users and developers of OpenPetra. OpenPetra is an open source software for the administration of charities.