This repository is a clone of "appbundler"

https://java.net/projects/appbundler

Arduino is currently using a patched version of appbundler that allows to set version number and file associations. You can see the patch applied in the "arduino" branch of this repository.

https://github.com/arduino/appbundler/commits/arduino

The patches were submitted upstream but they are unlike to be merged since appbundler seems to be phased out in favor of JavaFX.