YUI

All web developers would be glad for this to Yahoo. Distributed under the BSD Yahoo User Interface(YUI) library is a set of controls and utilities to develop rich web applications. The scoring point apart from the fact that we need not reinvent the wheel is its rich documentation which is generally the bane of most shared projects. So next time, you want a calendar control first go to YUI and check if they have already done your work. It's easy and really good. Click here to know more