TFW At our organization, we use Tcl/Tk to build graphical interfaces to interact with radar and electronic warfare systems. We generally create custom C libraries to interact with the hardware and use Tcl/Tk as the "glue" to bind the user interfaces to the libaries. We also use Itcl to create reusable components (e.g. loggers, consoles, editors) to allows us to rapidly create new applications. We also deliver these applications to our customers.
We have found that Tcl/Tk is perfect for our uses, the Tcl interpreter is very robust, the event loop provides the functionality of a threaded application without the headache, and the ease with which we can create cross-platform libraries and applications gives us the flexability we need to meet our customer's needs.