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
Obsidian is an extensible virtual world system with a fullblown multiplayer client-server architecture. It is not a VRML2 world system, though there are plans to include VRML2 as a world data format. Note that active development on this system stopped a while ago, though the code is still available for the curious. The code may not even compile on current Linux or Irix systems.
Oww (One-Wire Weather) is a client program for Dallas Semiconductor / AAG 1-wire weather station kits, providing a graphical (animated) display to monitor outside temperature, wind speed and direction, rainfall, and humidity. Extra temperature sensors may be added. A 1-wire "hub" may be used for improved reliability and range. Weather data may be logged to CSV files, parsed to command line programs, sent to the Henriksen Windows client, or uploaded to Web servers at Dallas, The Weather Underground, and HAMweather.
Orac is a GUI tool for Database Administrators written in Perl, Tk, and DBI. It organizes many useful DBA scripts into a nice graphical interface, for collecting statistics on your database, or diagnosing problems. It currently supports Oracle, Sybase, and Informix. Richard Sutherland's DDL::Oracle Perl module has been integrated with the current version for the Oracle side of things, greatly improving the Oracle developer options on the program.