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.
The SeaMonkey project is a community effort to develop an all-in-one Internet application suite. It contains an Internet browser, email and newsgroup client with an included Web feed reader, HTML editor, IRC chat, and Web development tools, and is sure to appeal to advanced users, Web developers, and corporate users. It uses much of the Mozilla source code powering such successful siblings as Firefox, Thunderbird, Camino, Sunbird, and Miro.
The Interverse is the evolution and combination of the Web, chat, instant messaging (IM), and voice communication. It is not just a graphical user interface (GUI), but an immersive user interface (IUI). The Interverse is a virtual universe running on top of the Internet. It uses the Crystal Space 3D engine to render the user's view of the world.
libircclient is a small but powerful library that implements the client-server IRC protocol. It is designed to be small, fast, portable, and compatible with RFC standards and most IRC clients. It includes multi-threading support, sync and async interfaces, CTCP and DCC support, and color support. Good documentation and examples are available.