WEKA, for Waikato Environment for Knowledge Analysis. With it, a specialist in a particular field is able to use ML to derive useful knowledge from databases that are far too large to be analysed by hand.
Apache Mahout is a machine learning algorithms focused primarily in the areas of collaborative filtering, clustering and classification. Mahout also provides Java libraries for common maths operations and primitive Java collections.It also supports Recommendation mining which takes user's behavior and from that tries to find items users might like
MLlib is a Spark implementation of some common machine learning (ML) functionality, as well associated tests and data generators. MLlib currently supports four common types of machine learning problem settings, namely, binary classification, regression, clustering and collaborative filtering, as well as an underlying gradient descent optimization primitive
CLIPS is a productive development and delivery expert system tool which provides a complete environment for the construction of rule and/or object based expert systems. Key features of clips are Knowledge Representation,Portability,Integration/Extensibility,Interactive Development,Verification/Validation,Fully Documented and Low Cost
LIBSVM and LIBLINEAR are two popular open source machine learning libraries, both developed at the National Taiwan University and both written in C++ though with a C API. LIBSVM implements the SMO algorithm for kernelized support vector machines (SVMs), supporting classification and regression.