KildClient is a MUD Client written with the GTK+ windowing toolkit. It supports many common features of other clients, such as triggers, gags, aliases, macros, timers, and much more. But its main feature is the builtin Perl interpreter. You can at any moment execute Perl statements and functions to do things much more powerful than simply sending text the the mud. Perl statements can also be run, for example, as the action of a trigger, allowing you to do complex things.

Website: http://kildclient.sourceforge.net/phpwebsite/