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.
LarryMessenger is a simple to install and easy to use cross-platform instant messenger client. It has a nice graphical user interface, and allows people to communicate over a LAN with static IP addresses without the need for a central server. Furthermore, it provides functions to query the ICQ and AIM networks.
OpenGaim is an instant messaging or "text chat" client capable of communicating over many protocols, including Jabber, AOL Instant Messenger (AIM), ICQ, MSN Messenger, Yahoo! Messenger, Internet Relay Chat (IRC), and more. It is a loose relative of the Gaim project and contains much of the source code in Gaim itself. However, OpenGaim aims to provide quicker releases to fix major problems, and advanced customization options and features not available in Gaim.