Hidden Markov Models software library from the Center of Applied Informatics, Cologne. Includes algorithms such as Viterbi, Baum-Welch, and Forward-Backward. [C, GPL license] http://sourceforge.net/projects/ghmm
Computational model of human language acquisition written in Java; currently acquires a protolanguage of nouns and verbs language based on visual perception http://sourceforge.net/projects/ebla
A propositional theory refinement system that will modify a incomplete or incorrect rule base so as to make it consistent with a set of input training examples. [Free] http://www.cs.utexas.edu/users/ml/neither.html
A site by Elad Yom-Tov, co-author of the toolbox, that contains additions and updates to the toolbox, as well as a discussion board http://www.yom-tov.info
Machine learning library for Observable Operator Models (OOMs) suitable for time-series and sequence data classification and prediction. OOMs are similar but more powerful than HMMs. [C++, BSD license] http://omk.sourceforge.net