4chan X is described as 'Script that adds various features to anonymous imageboards. It was originally developed for 4chan but has no affiliation with it' and is an app in the web browsers category. There are 2 alternatives to 4chan X for Google Chrome, Pale Moon, Violentmonkey, Mozilla Firefox and Tampermonkey. The best 4chan X alternative is 4chan XT, which is both free and Open Source.
4chan XT was originally forked from 4chan X for this PR, It is a migration of 4chan X from coffeescript to TypeScript/JavaScript. It is named XT both as a continuation of eXTended, and a T for TypeScript.
Dollchan Extension is the userscript and extension that combines various options & features, making you hang out on imageboards in an easier and more convenient way. If you have visited sites like 4chan.org or 2ch.hk, then you probably already heard about it.
