Tk sources for 8.4 include a labelframe. (This was added at 8.4a4(?).)
LV: http://purl.org/tcl/home/man/tcl8.4/TkCmd/labeledframe.htm should be the page - but for some reason is not currently present - we have contacted the activetcl team to see what is up.
GPL: but http://purl.org/tcl/home/man/tcl8.4/TkCmd/labelframe.htm works and seems to me the correct URI.
Category Command - Tk syntax help - Arts and crafts of Tcl-Tk programming