Tcl/Tk is a combination of scripting language Tcl ("Tool Command Language") and graphical user interface toolkit. Tcl/Tk is available as a cross-platform freeware, and widely used for rapid prototyping and scripting applications.
Download Active Tcl/Tk (distributed by ActiveState Software Inc.).
Examples of using QuickField with Tcl/Tk:
Relay dynamics simulation using Tcl/Tk and ActiveField (QuickField Object Model)
Relay dynamics simulation using Tcl/Tk and Parametric command line