Tcl/Tk extensions for POSIX systems TclX is a set of extensions which make it easier to use the Tcl scripting language for common UNIX/Linux programming tasks. TclX enhances Tcl support for files, network access, debugging, math, lists, and message catalogs. TclX can be used with both Tcl and Tcl/Tk applications. Install TclX if you are developing applications with Tcl/Tk. You'll also need to install the tcl and tk packages.