Apache Cassandra is a decentralized, Elastic Cassandra highly scalable second-generation distributed database. It is meant to run on a cluster of nodes, but will run equally well on a single machine. Cassandra uses Thrift for its external client-facing API.
As reported by Emgin.com, although the version number released was 0.6.0, Apache Cassandra 0.6.0 is considered a stable release that is well tested and reasonably free of serious problems, or at least the problems are known and well documented.
Apache Cassandra is a free open source software licensed under the Apache License, Version 2.0."