K.E.T.T.L.E (Kettle ETTL Environment) is a meta-data driven ETTL tool. (ETTL: Extraction, Transformation, Transportation & Loading)

This means that no code has to be written to perform complex data transformations.
Environment means that it is possible to create plugins to do custom transformations or access proprietary data sources.

Kettle is released under the Apache License v2.0 since version 4.3.0.

Kettle moved to GitHub at the beginning of 2014: http://github.com/pentaho/pentaho-kettle
This move could lead to strange results in the Ohloh metrics.