Yahoo wants to be your friend

Yahoo has released some of it's AJAX tools for developers to use (for free).

The Yahoo! User Interface Library is comprised of a number of dynamic HTML utilities and controls for building rich web UIs and Ajax applications. They are made available under an open-source license. In addition, Yahoo! released the Yahoo! Design Pattern Library . This collection of design patterns for Web interaction is intended to provide Web designers prescriptive guidance to help solve common design problems on the Web.
The list of components includes:

* Calendar
* Slider
* TreeView

but does not appear to include a text editor or a DataGrid.

Yahoo! Developer Network

Other available AJAX libraries:

Google
Prototype
Blueshoes