jquery-slimscroll-rails

https://github.com/marcosnogueira/jquery-slimscroll-rails

slimScroll is a small (3.7KB) jQuery plugin that transforms any div into a scrollable area with a nice scrollbar - similar to the one Facebook and Google started using in their products recently. slimScroll doesn't occupy any visual space as it only appears on a user initiated mouse-over. User can drag the scrollbar or use mouse-wheel to change the scroll value.