Licq includes all the basic features of ICQ, like sending/receiving messages, chat, file transfer, contact list with pixmaps and user status, basic/extended user info, adding/editing users from within the GUI, user history, user groups, and new user registration. All commands and information are available through a simple and convenient tab dialog. Licq also has a completely configurable user interface with Skin and Icon pack support. It is written in C++ and comes with a GUI plugin using the Qt widget set. Other plugins are also available, like basic MSN support.
climm (CLI-based Multi-Messenger) is a portable, small, yet powerful console-based ICQ and XMPP client. It supports password changing, auto-away, creation of new accounts, and other features that makes it a very complete yet simple client. It is able to send and receive messages from the ICQ network, list users that are offline and online (including their online status), search for users by email address, and look up basic (name, UIN, email) information. climm was formerly known as mICQ.
ickle is an ICQ2000 client using the GTK-- graphical toolkit. It aims to bring all the useful features of ICQ2000 to non-Windows users. It supports message/URL/SMS sending/receiving (including SMS delivery reports), status changes, reading away messages, and fetching advanced user info from a server. History browsing and lots of configurability in Settings are available.
YSM (You Sick Me) v7 is an ICQ console client. It was originally meant to run in Linux, but it has been successfully tested in Linux, BSD, Win32, BeOS, and QNX. The client requires no extra libraries, and is written in the C language. YSM is based on the last ICQ protocol version, v7/8.
SMSTerm is an application that uses the ICQ2000 protocol to present you a shell on your mobile phone which allows you to interact with your computer from any mobile on a GSM network. It runs a shell on a pty, and allows you to directly send commands to the shell through SMS. Minimal authentication is done over SMS before spawning a shell and offering it to the user on the mobile phone. It is very useful for remote administration tasks, or checking out the status of the network, or just to run some small chores on your system while you are away. It uses Expect.pm in the background. SMSTerm also includes a script to send SMS through the ICQ network from the command line to any GSM mobile, and also includes a PHP script to set up a Web->SMS gateway.
kicq is an ICQ client specifically designed for the KDE desktop. It has a simple, clean interface very similar to the original Windows ICQ client, and includes all of the most commonly used ICQ features such as messaging, real-time chat, and file transfer. It features complete message history, a New ICQ User registration window, multiple ICQ accounts, SOCKS5 proxy inline support, configurable sound events, Cyrillic koi8-r/cp1251 recoding, and support for the ICQ UDP v5 and ICQ TCP v2 protocols.