Extended Tcl is a superset of standard Tcl. Extended Tcl has three basic functional areas: A set of new commands, a Tcl shell (i.e. a Unix shell-style command line and interactive environment), and a user-extensible library of useful Tcl procedures, any of which can be automatically loaded on the first attempt to execute it.
In addition, a detailed help system is available for Tcl/Tk: tclhelp.