Perceptron is a rule-weighting algorithm based on artificial neural networks ("perceptrons") instead of ["GeneticAlgorithm"]s. It is based on error backpropagation by gradient descent and includes several security and accuracy-related modifications. It has replaced the GA in the RescoringProcess for SpamAssassin 3.0.
Some info may be found at [http://www.spamassassin.org/full/3.0.x/dist/masses/README.perceptron masses/README.perceptron] and at RunningPerceptron.