A quick look at every link that's been added thus far.
Multiple protocols, dozens of apps, dozens more use cases. So where do you or I start? It's simple I promise. Mayhaps a little overwhelming to see this quick post alongside 50 and counting...

Session | Send Messages, Not Metadata. | Private Messenger
Session is a private messenger that aims to remove any chance of metadata collection by routing all messages through an onion routing network.

NextGraph - Decentralized, encrypted and local-first platform and framework, towards the better internet we all deserve!
Features a social network, shared documents, productivity tools, an app store, and more! You can use NextGraph for free : resilient, secure, private and encrypted. You own your data and software! Developers can build new web3.0 local-first apps with our open source framework, based on open standards, with CRDTs, E2EE, Linked Data, JSON, Markdown...

Freenet
Freenet is a peer-to-peer platform for decentralized applications: communication, collaboration, and commerce without reliance on big tech. Your computer becomes part of a global network where apps are unstoppable, interoperable, and built on open protocols.


DSNP - Decentralized Social Networking Protocol
DSNP establishes a shared social layer no longer dependent on a specific app or centralized platform.
XMPP - The universal messaging standard
XMPP is the Extensible Messaging and Presence Protocol, a set of open technologies for instant messaging, presence, multi-party chat, voice and video calls, collaboration, lightweight middleware, content syndication, and generalized routing of XML data.


Zot, Nomad, and Nomadic Identity in the Fediverse
ForgeFed
ForgeFed is a federation protocol for software forges and code collaboration tools for the software development lifecycle and ecosystem. This includes repository hosting websites, issue trackers, code review applications, and more. ForgeFed provides a common substrate for people to create interoperable code collaboration websites and applications.

IPFS: Building blocks for a better web | IPFS
Open protocols to store, verify, and share data across distributed networks.
Explore Nostr Apps
Join your peers in a healthy social network. Nos is our Nostr client for humans, not algorithms.

Nostr - Notes and Other Stuff Transmitted by Relays
Nostr is an inclusive communication commons. A simple standard that defines a scalable architecture of clients and servers that can be used to spread information freely. Not controlled by any corporation or government, anyone can build on Nostr and anyone can use it.
Solid: Your data, your choice - Solid Project
Solid is an evolution of the web by its creator Sir Tim Berners-Lee. Solid realizes Tim's original vision for the Web as a medium for the secure, decentralized exchange of public and private data.
OStatus Community Group
OStatus is a suite of protocols that lets people on different social networks interact. This group will develop the next version of the protocol.