ClicksAndWhistles is a free IRC client that supports multiple account logins, floating windows, multi-server connections, UTF-8 support, customizable text and paragraph formatting, customizable colors, styles/themes, and backgrounds. It also supports PNG images, outline/shadow fonts, bookmarks, and customizable message strings.
It supports macros, script execution after connection, and keyword highlighting...
Compared to other clients, ClicksAndWhistles is compact but no less functional than mainstream clients like mIRC.