Apache Mahout - Distributed Linear Algebra
WEKA - WEKA is a set of powerful data mining tools that run on Java.
KNIME - KNIME, the open platform for your data.
Orange - Machine learning for novice and experts.
RapidMiner - RapidMiner is a software platform for data science teams that unites data prep, machine learning, and predictive model deployment.
KEEL - KEEL contains classical knowledge extraction algorithms, preprocessing techniques, Computational Intelligence based learning algorithms, evolutionary rule learning algorithms, genetic fuzzy systems, evolutionary neural networks, etc.