I started writing Trebuchet when I became frustrated at TinyFugue's text-only interface, and at the lack of any GUI MUD clients that were both easy to use, and as powerful as TinyFugue. What I consider nice about it may not even be interesting or useful to other people. Yet it's amazingly fast. You can create Hilites and Triggers that watch incoming text from the world. They can highlight all or part of each line, send automated commands back to the MUD, or even run TCL scripts.
Triggers is very flexible.
Highlight Styles can include text color, background color, font, size, bold, italic, etc. Highlight Styles can have StyleMenu entries associated with them, that pop up in context menus when you right-click on the highlighted text. You can create command line Macros that can take multiple arguments and expand them out to much more complicated commands or TCL scripts. You can create QuickButtons that can send commands or execute TCL scripts with a single click. You can create KeyBinds to let you send commands or execute TCL scripts, with just a few keystrokes.