[ excerpt from developer's site ]

SpamOracle, a.k.a. "Saint Peter", is a tool to help detect and
filter away "spam" (unsolicited commercial e-mail). It proceeds by
statistical analysis of the words that appear in the e-mail, comparing
the frequencies of words with those found in a user-provided corpus
of known spam and known legitimate e-mail. The classification
algorithm is based on Bayes' formula, and is described in Paul
Graham's paper, A plan for spam.

WWW: http://cristal.inria.fr/~xleroy/software.html