non-linear regressions

["govindan subramanian" <vaishnavi66 "at@at" hotmail.com>]

 Dear CCL'ers
I am interested in knowing about any freeware/shareware for performing
 non-linear regressions in UNIX/Windows platform.  My immediate interest
 is
 to perform sigmoidal fitting.  Any possible indicators are welcome.
 Will
 summarize if there is sufficient interest.  Thanks.
 -subramanian.g
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