As the economy totters, it’s easy to make fun of the concept of “Web 2.0” — the rallying cry of a generation of chipper start-ups spawned over the last few years with an unusual aversion to vowels.

Certainly, most of the venture capitalists I’ve talked to at the Web 2.0 Summit have said they are shying away from companies that are based on the idea of growing an audience now and figuring out how to make money later. However, after listening to the presentations here over the past three days, it is clear that some of the key concepts of the Web 2.0 movement are, in fact, taking root in deep ways.

One of the most significant trends is how the big companies that make very complicated systems are reworking them using the principles of Web 2.0 companies, particularly the notion of programs that talk to other programs. They are breaking up their technologies into discrete modules that can work alongside data and applications from others.

Facebook can be credited with taking the first step to open up large parts of its service to third parties. Last year, it let their applications on its site. Now, through its upcoming Facebook Connect service, it will let other companies build applications that use its list of people and who their friends are to deliver new services.

Yahoo, a vastly more complex site, is restructuring to allow others to use many parts of its service: the content, the search engine, the social relationships embedded in e-mail, and such. That means that Yahoo information can be used on other sites, and developers can create applications to run on Yahoo. “If and when we can get our 500 million users on our platform, the power is huge,” Jerry Yang, Yahoo’s chief executive, told the conference. This, of course, involves reworking much of the software behind the site in order to connect politely and consistently with other companies.

Not to be outdone, Dave Girouard, who manages Google’s efforts to sell services to big enterprises, said that Google, too, developing a platform. “We want to you to have the same access to Google that our internal developers do,” Mr. Girouard said. He offered no details.

In a completely different market, Salesforce.com is transforming itself from service dedicated to tracking sales leads to a platform that allows many more options. Marc Benioff, its chief executive, told the conference about the company’s new platform, Force.com. Now customers can run their own applications on Salesforce’s computers, mixing its systems with those from other developers. The point is to help companies develop internal systems, Web sites for the public and even applications to run on social networks like Facebook.

By far the most ambitious effort along these lines is Microsoft’s new operating system called Azure, which is being developed under the direction of Ray Ozzie.

In the broadest sense, Azure is a system that enables a program to run on personal computers, on mobile devices and on Microsoft’s own data centers without losing track of important data. But as I talked to Azure’s developers here, it was clear that Microsoft is trying to incorporate both strands of Web 2.0 thinking into the new operating system.

First, it is designed to interact with many other systems. It can pull in data from other places and formats and create widgets that add features to Web sites. Microsoft insists that Azure will be more respectful of the various standards used on the Internet than the company’s other products have been.

Moreover, Microsoft has built what it claims are industrial-strength versions of some of the social features common to Web 2.0 applications, such as a combined list of updates modeled after the Facebook newsfeed but designed to keep track of relationships among hundreds of millions of people.

It’s too early to say which, if any, of these big-company efforts to build platforms will succeed. Some may well collapse of their own complexity. Others may be attempts by their creators to chase buzzwords. In 2001, you wouldn’t have been able to predict the Web sites that would prevail.

But I do think that we can count on moving into a world where very complicated computer systems are designed to talk to people and to each other, using the ideas developed in the Web 2.0 era, with or without vowels.