Core concepts that underpin all P2P systems.

Overlay Networks and DHTs — Kademlia, Chord, structured vs unstructured overlays, DHT modes, routing hardening

Transport and Connectivity — TCP, QUIC, WebRTC, NAT traversal (ICE/STUN/TURN), relays, transport security, multiplexing

Content Addressing — Merkle DAGs, CIDs, chunking strategies, mutable pointers over immutable data

Storage and Distribution — Swarming, caching, pinning, erasure coding, incentive mechanisms

How peers exchange messages and synchronize shared state.

Real-time Messaging and PubSub — Gossip protocols, GossipSub, topics and discovery, ordering and reliability

State Sync and CRDTs — Eventual consistency, CRDT families (state/op/delta), append-only logs, anti-entropy

Identity, authorization, privacy, and defense in adversarial networks.

Identity and Capabilities — Keys as identity, DIDs, UCAN, macaroons, capability-based security, authorization models

Privacy and Anonymity — The privacy spectrum, onion/garlic routing, metadata reduction, name systems, trade-offs

Security Threats and Mitigations — Sybil, eclipse, spam/DoS, content poisoning, traffic correlation

Patterns, testing, and governance for building and running P2P systems.

Design Patterns — Content-addressed networks, rendezvous, superpeers, edge-first, layered architecture, defense in depth

Testing and Operations — Simulation, NAT labs, security testing, telemetry, upgrades, operational checklists

Compliance and Safety — Legal considerations, abuse handling, safety by design, the anonymity dilemma

Production P2P stacks and protocols, each with deep links to the concepts above.

libp2p — Modular P2P networking stack (Go, Rust, JS, Nim) used by IPFS, Ethereum, Polkadot

IPFS and Filecoin — Content-addressed hypermedia protocol and verifiable storage marketplace

BitTorrent — Swarming file distribution, tit-for-tat incentives, DHT, magnet links

Hypercore — Append-only logs, Hyperdrive, Hyperswarm, Autobase, Keet

Secure Scuttlebutt — Social-graph-based replication, offline-first social networking

Matrix — Federated/P2P messaging, E2E encryption, room state DAGs, Pinecone

Tor and I2P — Anonymity networks, onion/garlic routing, hidden services

Other Notable Systems — GNUnet, Freenet/Locutus, Tahoe-LAFS, Syncthing, Nostr

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See also the original single-page P2P Technologies Knowledge Base for a compact reference.