Stylebot - Change the appearance of websites instantly. Preview and install styles created by other users on stylebot.me
Greasy Fork - A site for user scripts.
Dark Reader - Reduce eye strain in your browser with this extension that provides a dark theme for browsing.
Violentmonkey - Violentmonkey is a userscript manager to support running userscripts in web pages.
Stylus - User Styles Manager - Stylus is a userstyles editor and manager based on the source code of Stylish version 1.5.2.
Userscripts - An open-source userscript editor for Safari.