http://sf.net/projects/incrtcl/ is where the CVS for iwidgets is maintained.
In the early life of itcl/itk/iwidgets, they were all three distributed in the same source tar file.
During 2001, a TIP was submitted proposing that the incr tcl be included as an extension distributed with Tcl.
If/when this proposal is implemented, users will need to download the tcl, tk, itk, and iwidgets tar files to get the pieces to use iwidgets.
See incr Widgets for a list of the widgets included in the set. [What do we do about the cases below which overlap with widgets that already existed in Tk, etc.?] In the case of overlap, just update the associated page with info about each of the items, and the extension with which it is associated.
This package is part of the ActiveTcl Batteries Included distribution.