Great job Daniele.
Sorry for not answering earlier. What you have done can be simplified and you don’t need to use install4j.
In the snap-engine-kit module is an assembly defined. This assembles all the necessary jars into one zip file.
Move into the directory snap-engine/snap-engine-kit and execute on the command line
mvn clean package assembly:assembly.
This will create the snap-engine-<version>.zip file.
This zip contains three directories lib, modules and licenses.
The s3tbx modules need to be added manually to the modules dir.
Also I have just updated this assembly to include scripts (in a 4th directory ‘bin’) to start gpt from the shell.