libpurple

libpurple is a multi-protocol instant messaging library that provides the core functionality shared by many chat clients. It implements user authentication, presence, contact lists, messaging, chat rooms, file transfers, and avatars, while leaving the user interface to client applications. libpurple is the backbone of Pidgin, and it is also used by other applications such as Adium and Kopete as a backend.

Written in C, libpurple offers a plugin-based architecture in which protocol support is added through protocol plugins. The library defines common data structures and APIs for accounts, buddies, conversations, and messages, and manages network connections, event handling, and state synchronization. It is designed to be embeddable, allowing applications to reuse its functionality without duplicating protocol code.

Protocol support is provided by a large collection of plugins; some of the most widely used include XMPP (Jabber), IRC, AIM, ICQ, MSN, Yahoo, and Google Talk, among others. New protocols can be added by developing additional plugins, keeping the core library protocol-agnostic.

libpurple originated from the Gaim project and was integrated into the Pidgin ecosystem. It is released under the GNU General Public License, and is maintained by an open-source community of contributors.