People often ask about combinations of gnuplot
[ftp://ftp.gnuplot.vt.edu/pub/gnuplot]
and Tcl; in fact,
archives from [the comp.lang.tcl newsgroup] 
pertaining to gnuplot are quite extensive
[http://groups.google.com/groups?q=gnuplot+group%3Acomp.lang.tcl*&num=25&hl=en&scoring=d].
Perhaps the most impressive marriage of the two is
UniGNUPlot
[http://unicalculus.sourceforge.net/unignuplot/],
which makes for quick development of useful graphs:

"Just with simples 'click' and scroll bars,  
you have a good graphic in seconds, ready to insert
in the document what you want or directly to the printer..."