X-Chat, commonly written XChat or xchat, is one of the most popular IRC clients for Unix-like systems. It is also available for Microsoft Windows and Mac OS X (via an offshoot of the project, called X-Chat Aqua, which keeps in sync with the main development branch and is much more popular than the official version maintained by the Fink project).
It has a choice of a tabbed or tree interface, support for multiple servers, and a high level of configurability. Both command line and graphical versions are available, although use of the graphical version far outweighs use of the command line version.
X-Chat Features
Lightweight - Very samll installatoin files
Plugins supported
Tabbed interface
High Level of Configurability
Graphical and command line version availability
X-Chat is property of Peter Zelezny. These downloads are 30 day free trial.