>Tcl/Tk to this day is the best tool to make GUI frontends for CLI applications.

Why? Please elaborate. I've heard others say this, but would like to know more.

>Besides that, in the past I used it in production for intranet database entry applications.

GUI apps?

> Why? Please elaborate.

Tk's GUI object model is sitting at a reasonable maxima between trivial to make use of vs. triggering the events necessary to make the GUI active.

Small example. You want a button on your GUI that triggers a procedure called "process" when it is clicked, this is the code you need (if you are fine with the remaining defaults) (and assuming you used 'pack' as the geometry manager):

    button .process -text "Process Entries" -command process
    pack .process -side top

> Why?

CLI applications typically read text from stdin and write text to stdout. The tcl model of "everything is a string" makes exactly the right abstraction to create GUI frontends for CLI applications rapidly and keep them simple at the same time.