NetPlug is an extensible multi-connections, multi-protocol, network client program, written in pure Tcl/Tk. Includes a complete Irc client plug in that you should love if you like IrcII 'classic' look & feel (plus customizable style/colors scheme, sound,... Now includes full DCC support (with GUI), ircII like aliases and improved scripting (Tcl!), keywords (your nick...) highlighting, and more
OpenIsis provides a library and tools to access CDS/ISIS databases, which are mostly used for bibliographic data (ISO2709, Z39.50) but also well suited for other catalogues due to the very flexible indexing mechanism. Based on a C library, there are also bindings for Perl and Java (Tcl to come).
Pixane is an image processing library for Tcl that allows the scripting of all kind of image transformations. It supports reading from and writing to a large set of file formats (JPEG, PNG, GIF, BMP, WBMP, etc) and provides anti-aliased text rendering and a set of built-in fonts. It doesn't requires Tk, so it can be used to easily generate images dynamically from CGI. Binaries are provided for many platforms as dynamic libraries with no external dependencies for easy deployment. It is also a core component of the eTcl distribution.
SMM++ Mud Client is a mud client with extended and unique features. Aside from all standard mud client functionality like ANSI color support, aliases, action triggers, and tab-completion, SMM++ features a highly-customizable user interface (labels, buttons, and menus) and unique and powerful mapping capabilities, and SMM++ is the only mapping crossplatform (Tcl/Tk based) mud client available.