Standard Tcl Library:
Tcllib is a collection of utility modules for Tcl, all written entirely in Tcl (no compiling required).
These modules provide a wide variety of functionality, from implementations of standard data structures to implementations of common networking protocols. The intent is to collect commonly used function into a single library, which users can rely on to be available and stable.
Tklib contains utility modules that depend on Tk.
BWidget is a Tcl/Tk script-only set of megawidgets designed to provide the developer additional tools.
Tclapps is a set of demo applications written in Tcl, it notably includes TkChat.
Tclbench is a set of tools to compare performances between different Tcl and/or Tk versions.