The content assist script is a great little feature and so easy to add to a page that lets you popup a small window whilst typing into a textarea or input box with a list of words that match the currently typing word. An example of usage for this could be on a site search, this could show the latest, or most popular searches that match the currently input string so far. Think of it as a "type-ahead" feature.
Try typing 'a' to get you started.
Source code available at GitHub. Original found