Sideshow is a powerful javascript library which aims to reduce your user's learning curve by providing a way to create step-by-step interactive tours. Explain the features of your application, control your end-user's interaction with your UI, emphasize what you're explaining in each step by masking it. Just think! The sky is the limit!
If there are multiple steps for the same subject, sideshow fades it out then back in again, which is unnecessary and looks a bit odd