Apache Spark is a fast and general cluster computing system. It provides high-level APIs in Scala, Java, Python and R, and an optimized engine that supports general computation graphs. It also supports a rich set of higher-level tools including Spark SQL for SQL and structured data processing, MLLib for machine learning, GraphX for graph processing, and Spark Streaming.
For more information, see:
The Spark Homepage
The Spark Wiki and How to Contribute to Spark
Spark's Github Repository