Friendica is a decentralised social network that anyone can run on their own server. It offers posts, comments, photos, events and profiles, with access lists per item so that users decide who sees what. It federates with ActivityPub services such as Mastodon, with the diaspora* protocols and OStatus, and can bring in RSS and Atom feeds and email conversations. Written in PHP, it runs with MySQL, even on shared hosting; people either join a public server or install their own.
Friendica is free software under the AGPL-3.0 licence, developed in the open on GitHub by a community rather than a company, so no vendor sits between an organisation and its data. Each server is run independently, so data location and jurisdiction depend on who hosts it. An organisation can run its own server in an EU data centre, or choose a public server after checking its operator and country. Posts shared with other servers are copied there and fall under those operators' rules. Running a server means handling updates, moderation and backups.