Ajax is becoming popular for building interactive Web applications, so much so that a group of vendors is trying to ensure it gets implemented uniformly.
With Ajax, active parts of the page seek more data from an Internet server or validate data entered by a user, without requiring the user to stare at an hourglass symbol as the page goes back to a server. Google Maps is based on Ajax. The map fills out in the direction of the user's cursor movement because Ajax is detecting the movement and downloading more data from the map server, without the user specifically requesting it.
Google had to invest heavily to get Maps to perform consistently across different browser windows. That's why Google and others backed IBM last week when it announced it was donating software that will allow developers to work with Ajax on the Eclipse programmer's workbench. In effect, code developed with Rico, Dojo, or Zimbra, three popular Ajax toolkits, can be imported into Eclipse, run there for review and inspection purposes, debugged, and made ready as part of a larger Web application.