Tablesaw (https://github.com/jtablesaw/tablesaw) is Java dataframe begun in 2015 and is under active development (2018). It's designed to be as scalable as possible without sacrificing ease-of-use. Features include filtering by rows and columns, descriptive stats, map/reduce functions, cross-tabs, plots, machine learning. Apache license.
In one query test it returned 500+ records from a 1/2 billion record table in 2 ms.
Contributions, feature requests, and feedback are welcome.
