CT - Hi, I would like to ask the gurus out there if there is a sensible way of getting tcl to run only one instance of a script or application that works on all the platforms that tcl does.  Thanks.

[AM] I do not quite understand your question. Could you describe what you mean by 
"only one instance" ? Do you by any chance mean "one script that works everywhere"?
Or are there any other aspects, like particular directories ....?