Purpose: to discuss items known as calendar in the Tcl world.
Unfortunately, this name is used both as a widget that is part of incr Windows as well as a package in tcllib.
Docs for the iwidgets widget can be found at http://incrtcl.sourceforge.net/iwidgets/iwidgets/calendar.html and http://purl.org/tcl/home/man/iwidgets3.0/calendar.n.html
The tcllib group of modules contains some calendar support code. It does not yet have any reference docs though.
BLT comes with a calendar example and efftcl has a calendar example.
Category Command, a part of incr Widgets Category Package, subset Tcllib