http://tcllib.sourceforge.net/doc/ident.html
RFC 1413 [L1 ] specifies an "identification protocol" to answer the question, "who services port NN on host HH?"
Philip Moore has written a client that he likely will contribute to tcllib around June 2003.
DKF: Hardly anyone hosts an identd these days, BTW. It seems to have been dropped as revealing too much information about the system providing it...