Purpose: document such Tk "widget sets" as the following. Please feel free to add more info, create specialty pages containing additional details, etc. point to reference material or images of the widgets, mention the platforms, etc.
BLT is a C based widget library adding visualization and other helpful Tk widgets. See http://www.tcltk.com/blt/ for more details.
BWidgets is a Tcl/Tk based widget library that is stored as a separate module of http://tcllib.sf.net/ .
efftcl includes a number of useful Tk widgets. See [add url] for more details.
[incr Tk] is a C based megawidget framework based on [incr Tcl] for combining Tk widgets into more useful forms. [incr Widgets] is a collection of such useful widgets. See http://incrtcl.sf.net/ for more details.
POOL http://www.purl.org/NET/akupries/soft/pool/ is a personal library of routines, including caledar widgets, megawidgets, etc. (code useful for either GUI or just Tcl programming).