Tcl/Tk is perhaps the most mature of the dynamic languages, dating back to 1988. The evolution of the language over the last 20 years has been marked by passionate preservation of the balance between maintaining simplicity and utility with the adoption of new ideas and new techniques based on accumulated experience.
Tcl/Tk is used in a number of prominent software systems including DejaGnu (e.g. used for testing the gcc compiler), Expect and AOLserver. The language is used by many scientific organizations including NASA as well as being used extensively in the commerical and financial sectors. ( http://wiki.tcl.tk/20832 )