GNUnet

A peer-to-peer, serverless instant messenger and cryptographic network library focused on security and privacy.

Freenet is a peer-to-peer platform for censorship-resistant communication and publishing, providing a distributed, encrypted, decentralized datastore.

RetroShare is a decentralized, private, secure, cross-platform communication toolkit for sharing files, chat, messages, forums, and channels.

Chitchatter is a decentralized, end-to-end encrypted peer-to-peer communication tool for private chat, video, screen sharing, and file transfer.

OnionShare is an open source tool for securely and anonymously sharing files, hosting websites, and chatting over the Tor network.

A Node.js BitTorrent tracker implementation with both client and server components.

Lightweight, cross-platform BitTorrent client.

ENiGMA½ is a modern, highly customizable BBS software with support for traditional terminal access and web-based services.

An open source instant messaging transport that lets users chat across different IM networks.

Syncthing is a continuous file synchronization program that keeps files in sync between two or more computers.

A free, decentralized, federated video platform for hosting, sharing, and livestreaming videos.

qBittorrent is a BitTorrent client built in C++/Qt and powered by libtorrent.