Just following, the eXtensible Markup Language (XML) was developed in 1996. Simply put, XML is a markup language (not a programming language) that is used to define and describe data.
While these two languages have been around for quite some time, it has only been during recent years that people have discovered the potential made possible by combining them.
In order to demonstrate how cool AJAX can be, I created an AJAX-based Instant Messenger (click here).
The term "Web 2.0" is being used to describe where we are headed once all web-based applications are using AJAX to interact with users. Imagine the possibilities...