If you're reading this, you are probably already using Mastodon or another Fediverse-connected service, and you probably understand why it's problematic to put one big company in charge of everyone's data. Why not take that a step further and free yourself from other exploitative web services? Here's a list of the most useful free (libre) and open-source web services that I know of. It's definitely incomplete, but hopefully it's a start. (Boosts welcome!)

The Fediverse

• Mastodon - Needs no introduction. The federated microblogging platform positioned as a Twitter replacement. Similar services: Misskey, Akkoma
• Friendica - An advanced macroblogging platform which connects lots of different social networks - in addition to Mastodon, Friendica federates with the Diaspora network, and can be used as an RSS reader, as well as a client for e-mail and Twitter. Similar service: Hubzilla
• WriteFreely - A tool for hosting and following blogs. Similar service: Plume
• Lemmy - A link aggregation platform, similar to Reddit. Can also be used for forums. Similar service: /kbin
• PeerTube - A video sharing tool that uses BitTorrent to accelerate playback. Great YouTube alternative.
• Pixelfed - Tool for sharing photos and short videos, similar to Instagram.
• FunkWhale - Tool for sharing and listening to music and playlists, similar to SoundCloud.

Federated services

• Matrix - Decentralized, optionally encrypted instant messaging. DMs aren't at all secure here - admins and involved servers can easily leak them, even by accident - so it's worth having an account on Matrix for when that privacy is desired. Similar services: XMPP, IRC (unencrypted)
• Tutanota - One of many smaller email providers focused on security and software freedom.
• Diaspora - Another federated social network which is more mature, smaller, and more similar to Facebook.
• Libre.fm - Libre music sharing server which federates with Last.fm. The codebase is currently being completely rewritten, so you may want to wait and see how this changes.
• Mumble - Low-latency VoIP (voice chat/telephone) app

Multiple providers, but non-federated

• CryptPad - A collaborative office suite and cloud storage service, similar to Google Docs and Microsoft 365. Notable for its focus on end-to-end encryption for all files. Similar service: Nextcloud
• Gitea/Forgejo - Open-source hosting for open-source code, using Git and an easy-to-use interface. Soon to become federated! A popular general-purpose instance is Codeberg. Similar service: GitLab
• Searx/SearXNG - An ad-free and non-tracking search engine that aggregates results from all major providers. (Link goes to an instance list. About page contains links to the project page and a random instance selector.)
• Bitwarden - A cloud password manager with decent security. There is a flagship instance, but the various clients can be used with a third-party server, like vault.tchncs.de/. Also consider using KeePassXC locally.
• Jitsi - An encrypted videoconferencing platform that can be used anonymously.
• Hastebin - Free pastebin, for sharing temporary text or code snippets.
• LEAP Encryption Access Project - Several nonprofit VPN services using open-source software.

Frontends for proprietary services

• Nitter - JavaScript-free frontend for Twitter that doesn't track you.
• Invidious - YouTube frontend minus the anti-features. Several similar desktop and Android clients for YouTube exist - try out NewPipe!
• Libreddit - JavaScript-free private Reddit frontend.

Centralized, but source available

• Neocities - Personal website host, designed for uploading HTML/CSS/JavaScript files.
• Liberapay - Nonprofit-run donations platform similar to Patreon, and with no cryptocurrency. Not self-hostable for obvious reasons, but all code used is public domain.

Feel free to comment any good ones that I missed! I've explicitly excluded software designed exclusively for personal self-hosting, e.g. CMSes, from this list; this is targeted at people who are unable to self-host or code themselves. [参照]