Since someone's talking about Tk/tcl, I could talk a little about STk and guile (if anyone want's to hear about them). They're scheme interfaces to Tk. Scheme is a dialect of lisp. As an example application, I implemented a version of Tetris in STk. I doubt it could be written in Tk/tcl (without resorting to C programming, that is). I also have a call tree browser written in STk. Harvey