Apps with 'Userscript Manager' feature

Greasemonkey is a Firefox extension that allows you to customize the way webpages look and function.

Violentmonkey provides userscript support for Chrome, Opera, Maxthon and Firefox supporting most scripts for Greasemonkey and Tampermonkey.

Tampermonkey is a free browser extension and the most popular userscript manager for Blink- and WebKit-based Browsers like Chrome, Opera Next and Safari.

Firemonkey is a totally new combined user-Scripts and user-Style manager. While it has similar functions to other user-Script managers like GreaseMonkey/Tampermonkey/Violentmonkey, and user-CSS managers like Stylish/Stylus/xStyle, there are also differences.

Modify requests, inject JavaScript and CSS into pages.

Makeover lets you change the appearance and behavior of web pages with CSS and JavaScript. To use it, you go to a web page you want to customize, tap the Makeover icon, and paste the code into the text field.

An open-source userscript editor for Safari.

Quickly find and run your bookmarklets.

Customize the web with JavaScript or CSS.

Macaque is a UserScript Manager Browser Extension. Macaque provides you the ability to add, edit, remotely edit, as well as view the console logs for each UserScript!.

Greasemonkey Port is a userscript manager for SeaMonkey, originally written by Aaron Boodman and currently SeaMonkey front-end maintained by Marti, Ratty and/or Farby with some backend support from Anthony Lieuallen and Johan Sundström.