Documentation can be found at http://tcllib.sourceforge.net/doc/ncgi.html
The ncgi package provides commands that manipulate CGI values. These are values that come from Web forms and are processed either by CGI scripts or web pages with embedded Tcl code. Use the ncgi package to query these values, set and get cookies, and encode and decode www-url-encoded values. (From the man page [L1 ])
recently on comp.lang.tcl, aku mentioned that ncgi came about by starting with Don Libes' cgi.tcl extension and breaking the code into namespaces and 3 modules.
Related modules in tcllib are
Category Package, subset Tcllib