tksh is an implementation of the Tcl C library written on top of the library for the new KornShell (ksh93). tksh emulates the behavior of Tcl by using the API that is provided for extending ksh93, which is similar to the Tcl library in that it allows access to variables, functions and other state of the interpreter. This implementation requires no modification to ksh93, and allows Tcl libraries such as Tk to run on top of ksh93 unchanged, making it possible to use shell scripts in place of Tcl scripts. ksh93 is well suited for use with Tk because it is backward compatible with sh, making it both easy to learn and easy to extend existing scripts to provide a graphical user interface.
tksh is not yet another port of Tk to another language -- it allows Tcl scripts to run without modification using the ksh93 internals. This makes it possible to combine Tcl and ksh93, which is useful for writing ksh93 scripts that use components that have been implemented in Tcl (such as Tk widgets).
The latest tksh works with Tcl 7.6. The author is no longer working on this application.