Violentmonkey is one of several userscript managers, closely related to Greasemonkey and Tampermonkey, which provides userscript support for browsers supporting web extension APIs. This includes Chromium-based browsers such as Chrome, Brave, Edge, etc. as well as Firefox.
We choose to use Violentmonkey as addon of choice when creating user scripts/styles as it's opensource and well-maintained. Many scripts are also uploaded to a site called Greasy Fork, which is dedicated to hosting a large searchable collection of such userscripts for websites. Users can upload their userscripts there. Of course, whilst there are many useful scripts there, the number of scripts is so vast it may be a little hard to find the wheat amongst the chaff! Once you've installed a userscript manager into your browser, you can (aside from writing your own) find userscripts on Greasy Fork and install them into your browser easily.
Below are links to some of our scripts for various sites that have generally been written to address certain issues or niggles with look and feel.