Google's heft means that where it goes, developers follow. This year, the company has been an accidental catalyst for two major advances in Web application development: AJAX and mashups. Google didn't invent or evangelize either technology. It just quietly began making use of them, and the Web followed in its wake.

AJAX stands for Asynchronous JavaScript and XML (Extensible Markup Language), a term coined by Jesse James Garrett, the co-founder of user experience consultancy Adaptive Path. AJAX is essentially a bundle of Web standards and technologies that, together, enable greater application functionality to reside in a user's browser. Allowing more interaction to happen in the browser rather than on a remote server -- that's where the "asynchronous" part of AJAX comes in -- speeds up Web applications and helps them feel more like desktop software.

The technologies underpinning AJAX have been around for years. In a February 2005 essay posted online, Garrett described the AJAX design approach and cited Google as a high-profile practitioner: "Look at Google Maps. Zoom in. Use your cursor to grab the map and scroll around a bit. Again, everything happens almost instantly, with no waiting for pages to reload."

Garrett's essay kicked off a torrent of interest in AJAX. The tools were already there, but Garrett offered a framework for understanding how they could be used together, and helped developers recognize what it was Google was doing that made its services feel so different from other Web applications. Now, AJAX is starting to permeate Web development. Amazon's A9.com search engine and the Flickr photo-sharing Web site are two widely used AJAX-backed applications, but the real mark of AJAX's influence is the rapidly growing list of smaller Web application developers offering AJAX toolkits and incorporating its techniques into their software design.

Google was also a pioneer in bringing Web services to the masses, via "mashups" -- a term pinched from the music world, where it refers to compositions created by smushing together snatches of different songs. On the Web, mashups are new applications created by blending data and tools from different sources. Open APIs (application programming interface) and an assortment of standardized Web protocols make that possible. Companies like Yahoo, Amazon.com and even Microsoft have long made some of their APIs publicly available, but once again, it was Google that had the critical mass to spark a wave of developer innovation.

Google Maps was Ground Zero. Within weeks of Google Maps' debut, developers were creating custom overlays to blend the mapping service with outside data streams. HousingMaps.com brought in CraigsList.org real-estate listings and used Google Maps to illustrate the locations of advertised houses and apartments. ChicagoCrime.org used a public police database to add pop-ups pinpointing reported crimes in Chicago's neighborhoods. Other hacks blend Google Maps with weather information and lists of Wi-Fi hotspots, with a pedometer program, with traffic and weather reports, and even with a scavenger hunt game.

Mashups and AJAX are two of the technologies fueling what tech pundits call "Web 2.0." The idea holds that the Internet is in the midst of a transition from a collection of Web sites to a full-fledged applications platform, with deep interactivity and personalization potential. Give the technology a few more years to develop and achieve mass adoption, the theory goes, and the Web will become the new computing operating system.

From its position at the Web-development vanguard, Google is poised to continue trailblazing for the Web 2.0 vision.