I believe this app is only for Win 10. I do not know if it leaves registry keys behind or not or portable ?
GNU General Public License v3.0
Use this tool to:
Reduce the size of games (e.g. Fortnite: 18.8GB > 10.2GB)
Reduce the size of programs (e.g. Adobe Photoshop: 1.71GB > 886MB)
Compress any other folder on your computer
Visual feedback on compression progress and statistics
Configurable list of poorly-compressed filetypes that can be skipped.
Online integration with community-sourced database to get compression estimates and analyses
Integration into Windows Explorer context menus for easier use.
Analyze the status of existing folders
Shutdown/restart/sleep on completion.
there is a upx compactor av here already:
Upx is proned to be recognized by virus killers, not a good option.