That seems like a very niche thing, I’m happy with my 100% achievements and don’t want that status gone. What you could do instead is create a new steam account and steam family share your games to that new account to play again with no achievements.

That seems like a open source license to me? The main parts seem to disallow making money from it and commercial use.

More like JDownloader supports almost every download host website in existence without any hoops. Most other applications just support standard http downloads which may be difficult to use with many websites.