Apps to Federation

Funkwhale is a free and open-source, self-hostable platform for sharing music. It's a decentralized, community-oriented alternative to commercial music streaming services, built on ActivityPub for federation and offering features like music streaming, library management, playlists, and podcast support.

Openfire is a powerful, open-source instant messaging and group chat server built on the XMPP protocol. It enables real-time communication, collaboration, and presence management for individuals and organizations, offering robust features and a modular architecture for customization.

ejabberd is a robust, scalable, and modular XMPP application server designed for real-time communication, supporting a wide range of features including chat, group messaging, federation, and security protocols. Written primarily in Erlang, it's known for its high performance and reliability.

Gajim is a free and open-source instant messaging client for the XMPP protocol. Built using the GTK+ toolkit, it offers a wide array of features for secure and flexible communication, including encrypted chat, group conversations, multi-protocol support via gateways, and extensive customization options.

Rocket.Chat is a comprehensive free and open-source team communication platform, offering real-time chat, audio/video conferencing, screen sharing, and file sharing. Designed for flexibility, it can be self-hosted on-premises for maximum control and customization, making it ideal for organizations prioritizing data privacy and security.

Matrix is an open network for secure, decentralized real-time communication. It provides a flexible protocol for developers to build collaborative applications like instant messaging, VoIP, and video conferencing, enabling seamless communication across different service providers.

Pidgin is a free and open-source multi-protocol instant messaging client designed to connect users across various chat networks with a single application. It's highly extensible through plugins and supports a wide range of protocols including XMPP, ICQ, and IRC.