This is Tk version 8.5, a GUI toolkit for Tcl.

Tk is a graphical user interface toolkit that takes developing desktop
applications to a higher level than conventional approaches. Tk is the
standard GUI not only for Tcl, but for many other dynamic languages, and can
produce rich, native applications that run unchanged across Windows, Mac OS X,
Linux and more.

A full set of manual pages is also provided with this port.