envbot is an advanced modular IRC bot coded in bash. Features include SSL, IPv6, modularity (with several good modules already), transport modules (including OpenSSL, GnuTLS, netcat, etc.), loading/unloading/reloading of modules at runtime, rehashing configuration at runtime, advanced access control, and much more.
Based on ircu, Nefarious has features from various IRCds (Asuka, Bahamut, UnrealIRCd, and UltimateIRCd) with the intent of adding needed features to ircu without becoming too bloated or subject to anti-user behaviors. Most features can be activated or deactivated in the config file. Nefarious includes optional support for RBL-based blocking or marking, fakehosts, accounts, login-on-connect, half-ops, ban exceptions, mIRC color filtering chan-mode, network-wide bans (g-lines), and much more.
Off-the-Record (OTR) Messaging is a gaim plugin which allows you to have private conversations over the instant messaging system of your choice. It provides encryption, which prevents someone who intercepts your instant messages from reading them; authentication, which ensures that the correspondent is who you think it is; and perfect forward secrecy, which ensures that no previous conversation is compromised if you lose control of your private keys.
Akeni LAN messenger is a cross-platform instant messenger client. It is a P2P program that works on your LAN without the need of an Internet connection or a dedicated server. The client has an user interface similar to AIM, ICQ, or MSN Messenger. It supports all the standard IM features such as chat, group conference, presence management, file transfer, and emergency alert/notification. Extra features include contact management and optional tabbed chat sessions.
Baraza is a free mobile instant messaging server for Linux, supporting the Open Mobile Alliance's Instant Messaging and Presence Service (IMPS) protocols (also known as "Wireless Village"). IMPS is supported natively by a wide variety of mobile phones (particularly Nokia and SonyEricsson). The server also supports Jabber/XMPP messaging for inter-domain message exchange (a.k.a. federation).
BZFlag is a 3D, multiplayer, tank battle zone, capture the flag game that pits players against each other in a networked environment. It runs on Windows 95/98/NT/2000, Linux, MacOS 10.x, Irix, Solaris, and others. An OpenGL accelerator is highly recommended, but it is playable with 3D in software.