C programs of a particular type are known as big wish programs. They have this name because of their similarity to the wish program that is part of Tk.
Unless you are completely new to Tcl/Tk, you are familiar with the program tclsh. With tclsh you can interactively enter Tcl commands and see the results of their evaluation. Or you can name a script file for tclsh to evaluate. The Tcl interpreter within tclsh starts out with all the built-in command provided by the Tcl package.
The program wish is quite similar to tclsh. The primary difference is that the Tcl interpreter within wish starts out with all the built-in commands of both the Tcl and Tk packages. The commands of two packages combined in one interpreter right from the startup of the program.
Other examples include:
...and there are others.
more to come...