Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
Pidgin is a GTK2-based instant messenger application. It supports multiple protocols via modules, including AIM, ICQ, Yahoo!, MSN, Jabber, IRC, Napster, Gadu-Gadu and Zephyr. It has many common features found in other clients, as well as many unique features. Pidgin is not endorsed by or affiliated with AOL TimeWarner, Microsoft, or Yahoo.
KVirc is a Visual Internet Relay Chat Client based on the Qt library. Features include a MDI user interface, drag & drop, built-in scripting language (aliases, popups and events), customizable backgrounds and colours, DCC (chat, send with resume, voice), CTCP functions, mIRC colour support with preview, notify list, online help and configurable logging.
Beem is an XMPP (Jabber) client for Android. Beem is compatible with any standard XMPP server or service (including Ejabberd, Openfire, Facebook, or Gmail). It supports SASL, proxying (Socks4, Socks5, HTTP), DNS SRV, and chatting with a specific resource. Beem is available on the Android market and on the software's own Web site.
CodingTeam is a software forge that is lightweight and extensible. It provides a lot of collaborative tools. With this software forge, projects can benefit from basic features (such as screenshots, downloads, uploads, and news), communication features (such as chatrooms, forums, the OpenForge API, and Jabber/XMPP integration), and development features (such as a VCS code browser, a bug tracker, SVG statistics, timeline, and roadmap). Also provided are community tools (project browsing, tag clouds, notepad, and user profiles).