(Tool Command Language/ToolKit) Pronounced "tickle" or "ticklet," it is an interpreted script language that is used to develop a variety of applications, including GUIs, prototypes and CGI scripts. Created for the Unix platform by John Ousterhout along with students at the University of California at Berkeley, it was later ported to PCs and Macs. Safe-Tcl is an enhanced Tcl interpreter that provides a secure, virus free environment. Tcl also provides an interface into compiled applications (C, C++, etc.). The application is compiled with Tcl functions, which provide a bi-directional path between Tcl scripts and the executable programs. Tcl provides a way to "glue" program modules together. The Tk part of Tcl/Tk is the GUI toolkit, which is used to create graphical user interfaces. Other languages, including Perl, Python and Scheme, have incorporated Tk as well.