The installer is a JAR file, which is just a renamed ZIP file.
Use a standard unarchiver to extract libs/, roborumble/, robots/, and [roborumble/meleerumble/teamrumble/twinduel].sh into a folder.
libs/
roborumble/
robots/
[roborumble/meleerumble/teamrumble/twinduel].sh
Thanks! Done!