Ekstazi is a tool for Regression Test Selection (RTS) for Java.
If you have Maven, building Ekstazi should be trivial:
mvn install
At this point, most of the instructions are located on the official Ekstazi web page.
If you have used Ekstazi in a research project, please cite the research paper in any related publication:
@inproceedings{GligoricETAL15Ekstazi,
author = {Gligoric, Milos and Eloussi, Lamyaa and Marinov, Darko},
title = {Practical Regression Test Selection with Dynamic File Dependencies},
booktitle = {International Symposium on Software Testing and Analysis},
pages = {211--222},
year = {2015},
}