simplicity
slave interpreters
temporal arithmetic: The testimony of Tony Summerfelt is that, "if i need a program that does any kind of heavy duty date manipulation I use tcl. The clock command is easily my favorite in tcl."
Also see "idiom", "What is the advantage of Tcl over Perl", "Beginning Tcl", "Tcl warts", "Arts and Crafts of Tcl-Tk Programming", "Is white space significant in Tcl", "Tcl Heritage", "What is Tcl", "Tcl and other languages", Is Tcl different!...