StickyStack.js by mike-zarandona

An ultra-light jQuery plugin that tells you if an element is in the viewport but with a twist. Maintained by zeusdeux on GitHub, where it has earned 646 stars from the community.

viewport.jquery - simple but handy jQuery plugin adding methods and CSS selectors to check if element is in certain viewport. Maintained by xobotyi on GitHub, where it has earned 149 stars from the community.

Simple jQuery plugin to determine if an element is within the viewport. Maintained by moagrius on GitHub, where it has earned 120 stars from the community.