Optiscroll is an tiny and highly optimized custom scrollbar library for modern web apps.
Intence is a new UX concept and a JavaScript library which reflects the scrolling state in a simple and intuitive manner.
It highlights the scrollable area depending on the scrolling amount, thus efficiently explaining to a user what exactly can be scrolled, and is there much to scroll.
jScrollPane is a cross-browser jQuery plugin which converts a browser's default scrollbars (on elements with a relevant overflow property) into an HTML structure which can be easily skinned with CSS.