The Yahoo! User Interface Library (YUI) is a robust set of JavaScript controls and utilities for building interactive web applications. The library is released under the BSD license so it is free for use in all kinds of applications. Some of the available utilities include drag and drop, eventing, animation and a connection manager. The library controls include auto-complete, calendar, container, menu, slider, tree view and tab view.

Aptana is “The Web IDE,” a “robust JavaScript-focused IDE for building dynamic web applications.” It provides full code-assist and JavaScript debugging. It ships (that is, electronically) with some of the YUI libraries so you can quickly create projects leveraging YUI to try them on for size. Aptana is supported on Windows, Mac, Linux, and as an Eclipse plug-in (and thus virtually any modern platform).

I haven’t yet had the pleasure of using either of these tools but now that I know about them I hope to have the pleasure soon. If you’ve used them, tell me what you think.