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Please don't use Discord for FOSS projects
(drewdevault.com)
All about open source! Feel free to ask questions, and share news, and interesting stuff!
Community icon from opensource.org, but we are not affiliated with them.
Discourse, NodeBB and Flarum are all currently working on ActivityPub federation support. The first two have some basic support already available.
Edit: I read "decentralized". The "centralized" system for forums is obviously Reddit.