Mastodon
US alternative: Twitter/XDecentralized microblogging software and network that lets communities run their own social servers.
Open SourceFully European
Overview
Mastodon is free, open-source software for running federated microblogging servers that interoperate across the broader Fediverse. Users can join a server that matches their community norms or run their own, which prevents the platform logic from being captured by a single owner.