The source code for WiTS is available from the SourceForge repository.
WiTS is written in Tcl/Tk which is a simple yet powerful, cross-platform, open source programming language that has been used in a wide variety of applications over the last fifteen years. Tcl/Tk was originally developed by John K. Ousterhout for which he received the ACM Software System award in 1997.
To get started on Tcl/Tk, see Tcl Developer Xchange and Tcl Wiki.