Lemmy

ActivityPub for link aggregation

Is freely licensed?	✅
Decentralization	federated
User interface	gui
Target audience	end users system administrators
Platforms	gnu/linux bsd
Community support	chat
Website	https://join-lemmy.org
Source	https://github.com/LemmyNet/lemmy
NLNet grant pages	https://nlnet.nl/project/Lemmy https://nlnet.nl/project/Lemmy-PrivateCommunities https://nlnet.nl/project/Lemmy-Scale https://nlnet.nl/project/LemmyFed-AP

Lemmy offers a decentralized alternative to proprietary link aggregators like Reddit. School walkthrough (class board, not a public subreddit): Lemmy school scenario. Communities can self-host (Lemmy docs, configuration; examples only—not a canonical list):

koopa; setup docs · config example
long-running project instance
solar / climate community

Communities set their own moderation policies, votes are transparent, and ranking is not driven by a corporate engagement engine tied to surveillance and lock-in.