Getting started with AJAX

Nice article at Mozilla Developer Center on AJAX basics:

AJAX is a newly coined term for two powerful JavaScript features that have been around for years, but were overlooked by many web developers until recently when applications such as Gmail, Google suggest and Google Maps hit the streets.

Also, Ajax.NET is a free AJAX library for .NET developers. And Ajax Pages, SAJAX and OpenRico for ASP, JSP and PHP developers.