There are 3 repositories under userscript-management topic.
The home of FOSS user scripts.
Customize remote websites. This extension injects your Javascript- or CSS-based modifications on every visit. Also supports URL rewriting using regular expressions.
An open source user scripts repo built using Node.js
Userscript manager which based on Github Gist
A simple tool to manage userscripts (and userstyles)
Userscripts I made over the years, and used to be up on userscripts.org