Best open source userscript manager I've tried, it works well for my needs.

Violentmonkey is a great extension for anyone who wants to run userscripts in their browser. It’s open source, easy to use, and lets you customize websites with extra features or tweaks. Installing and managing scripts is simple, and it works smoothly without slowing down browsing. Perfect for users who like to personalize and enhance their web experience.

chrome cannot use it, so i use firefox instead