Apache Mahout - Distributed Linear Algebra
Datahike - A durable datalog database adaptable for distribution.
KNIME - KNIME, the open platform for your data.
Datomic - The fully transactional, cloud-ready, distributed database
WEKA - WEKA is a set of powerful data mining tools that run on Java.
Matisse - Matisse is a post-relational SQL database.