MLC++ Library / Utilities - http://www.sgi.com/Technology/mlc/

MLC++ is a machine learning library developed in C++. MLC++ is public domain and can be used free of charge, including use of the source code.
MLC++ contains common induction algorithms, such as ID3, nearest-neighbors, naive-bayes, oneR (Holte), winnow, and decision tables, all written under a single framework. It also contains interfaces to common algorithms, such as C4.5, PEBLS, IB1-4, OC1, CN2.
MLC++ contains wrappers to wrap around algorithms, including accuracy estimation (cross-validation, bootstrap, holdout), feature selection, discretization filters, automatic parameter setting for C4.5, bagging/combinining classifiers.
Object code for MLC++ utilities is provided for Silicon Graphic machines running Irix 5.3 or 6.2.

Note: This info converted from the original "The Data Mine" pages and pre-dates June 2001. Please remove this note if you update or check the info