NinjaKit is described as 'Yet another Greasemonkey available as Chrome and Safari extension' and is an app in the Web Browsers category. There are nine alternatives to NinjaKit for a variety of platforms, including Google Chrome, Windows, Firefox, Mac and Linux. The best alternative is Greasemonkey, which is both free and Open Source. Other great apps like NinjaKit are Tampermonkey (Free Personal), Violentmonkey (Free, Open Source), Stylebot (Free, Open Source) and FreeStylerWs (Free).
Greasemonkey is a Firefox extension that allows you to customize the way webpages look and function. Hundreds of scripts are already available for free. And if youre the tinkerer sort, you can also write your own.
Styles and skins for all popular sites in the web FreeStyler is a browser add-on that has everything you might need to style up websites you visit according to your taste. It provides a great number of ready-to-use styles with convenient system of managing them.