Here you will find some widely used and free (or shareware) data mining tools. Help yourself!
ADaM, Algorithm Development and Mining version 4.0 toolkit
AlphaMiner, open source data mining platform that offers various data mining model building and data cleansing functionality.
Databionic ESOM Tools, a suite of programs for clustering, visualization, and classification with Emergent Self-Organizing Maps (ESOM).
Gnome Data Mining Tools, including apriori, decision trees, and Bayes classifiers.
IBM Intelligent Miner. University scholars can now receive free copies of DB2 UDB and Intelligent Miner for educational or research purposes.
KEEL, includes knowledge extraction algorithms, preprocessing techniques, evolutionary rule learning, genetic fuzzy systems, and more.
KNIME, extensible open source data mining platform implementing the data pipelining paradigm (based on eclipse).
Machine Learning in Java (MLJ), an open-source suite of Java tools for research in machine learning.
MiningMart, a graphical tool for data preprocessing and mining on relational databases; supports development, documentation, re-use and exchange of complete KDD processes. Free for non-commercial purposes.
MLC++, a machine learning library in C++.
Orange, C++ components for data mining,includes preprocessing, modeling and data exploration techniques.
RapidMiner, a leading open-source system for knowledge discovery and data mining.
Rattle, a data mining suite based on open source statistical language R, includes graphics, clustering, modeling, and more.
StarProbe, Web-based multi-user server available for academic institutions.
TANAGRA, offers a GUI interface and methods for data access, statistics, feature selection, classification, clustering, visualization, association and more.
Weka, collection of machine learning algorithms for solving real-world data mining problems. It is written in Java and runs on almost any platform.