Since Greasemonkey is no longer being updated and /kbinStyles has been thriving, with people creating a lot of userscript for added functionality, I thought I should introduce Violentmonkey here. It is a really good opensource alternative for Tampermonkey and works well.
Supported browsers: Firefox, Chrome, Edge, Opera
You can check it out here: https://violentmonkey.github.io/
If you use any google service, take a look at Google Shut Up!