After Bill Gates

The two people most likely to carry on Bill Gates’ legacy also happen to be his biggest nemeses. Google founders Sergey Brin and Larry Page are already nerdy, brainy billionaires and are taking on Microsoft on multiple fronts—from search to online applications. And, in fact, when it comes to making money on the Web, it is Microsoft that is trying to catch up to Google.

Just like Windows is the starting point for everything people do on their PCs, for many people Google’s search engine is the starting point for everything they do on the Web. Brin and Page are building on top of that with online applications and other products aimed directly at Microsoft’s other businesses such as Gmail (Outlook), Google Docs (Office), and Android (Windows Mobile).  Sergey Brin profile | Larry Page profile 

Jeff Bezos, one of Seattle's other billionaires, is best known for bringing shopping online with Amazon.com. But over the past few years, Bezos has started selling something besides books and digital cameras. In his eyes Amazon.com is just a massive Web application that sits in the cloud.

He is now offering Amazon's "cloud computing" infrastructure to other companies that don't want to have to build their own data centers to store data or run a Web applications. Through a series of "Web services," companies can buy data storage, compute cycles, and database access from Amazon, and pay only for what they use. In this way, Bezos is helping to define the next era of Web-scale computing.  Jeff Bezos profile 

If there is one person who reminds people the most of the young Bill Gates, it is Facebook founder Mark Zuckerberg. The 24-year-old is a Harvard drop-out (like Gates) and is building his company with the focus and singular vision of making it the operating system for social applications.

The rise and success of Facebook is largely due to the fact that it is a platform for Web applications created by other developers (just as Windows is a platform for PC applications). And Zuckerberg has created a mini-economy around Facebook. Maybe these similarities are what convinced Microsoft to invest $240 million in Facebook last fall.  Mark Zuckerberg profile 

Marc Benioff (Salesforce founder and CEO) Just like consumer applications, enterprise software is moving to the Web as well. One of the first entrepreneurs to capitalize on this shift is Marc Benioff. His company, Salesforce.com, began by selling browser-based customer relationship management (CRM) software as a subscription service over the Web.

Taking a page from the Bill Gates playbook, he's extended his pay-by-the-drink concept to other areas of enterprise software and opened up Salesforce.com as platform for other companies to build and distribute their own Web-based software.  Marc Benioff profile 

A Ukrainian-born programmer, Max Levchin started his career as the co-founder and CTO of PayPal, which was sold to eBay for $1.5 billion in 2002. Two years later he founded Slide, which pioneered a new type of software known as a widget. Slide's widgets typically draw data from the Web and are geared towards self-expression. They can appear on your desktop or added to other Websites such as Facebook.

Slide's Facebook applications, which include FunWall and SuperPoke, boast more active users than any other company's. In January, Levchin raised $50 million for Slide, giving the company a valuation of half a billion dollars.  Max Levchin profile 

If software is becoming social, there is no better example than Digg. The popular news site attracts 15 million visitors a month, according to comScore. Digg relies entirely on its readers to submit headlines and links to articles, and vote them to the homepage.

Digg is the brainchild of founder Kevin Rose, who has mastered the art of teasing wisdom from the crowd. It is not so much about the underlying algorithms that power Digg as it is about setting the right conditions to give people the incentive to contribute.  Kevin Rose profile 

The Web at its core is a communications medium and Evan Williams keeps coming up with new ways to for people to communicate over it. He founded Blogger, one of the original and largest Web-based blogging services, which he sold to Google in 2003. More recently he co-founded Twitter, a micro-blogging service that lets people broadcast short text messages of no more than 140 characters.

By limiting the length of the messages, Twitter effectively lowers the barriers to communicating. After all, it is much easier to send a Tweet than to write an entire blog post.

The service is growing so fast that it is hitting serious scaling issues and is often down. But the company raised $15 million to help solve those issues. One of the investors: Jeff Bezos  Evan Williams profile 

Husband-and-wife team Stewart Butterfield and Caterina Fake created the most successful photo-sharing site on the Web with Flickr. By default, every photo uploaded to the site is public to encourage sharing and can easily be displayed on other sites as well. Flickr shows what can happen when you take personal media and put it online. Instead of being forgotten in a shoebox, a photo you took two years ago can be discovered and enjoyed by someone halfway around the world.

After it was purchased by Yahoo in 2005 for an estimated $35 million, Butterfield and Fake stayed on. The service kept growing and eventually replaced Yahoo Photos. It now attracts 54 million visitors a month worldwide, according to comScore. Both recently departed Yahoo, which is undergoing management turmoil, but keep an eye on them to see what they do next.  Stewart Butterfield profile | Caterina Fake profile 

On the Web, it can be hard to keep track all the information and services that are available. FriendFeed, a startup that launched publicly earlier this year, helps you manage the information overload by pulling together the online activities of all your friends in one place. You can see all of your friends' blog posts, Twitters, Flickr photos, stories they vote up on Digg, and YouTube videos they like, among other things, all in one feed. This turns out to be an effective, and addictive, information filter.

Two of FriendFeed's co-founders are ex-Googlers Paul Buchheit and BretTaylor. Buchheit was the 23rd employee at Google, where he created Gmail and implemented many of its innovative features. He developed the original prototype of Google AdSense, and was responsible for Google's famous "Don't be evil" motto. Taylor led the development of Google Maps and Google Local.  Paul Buchheit profile | Bret Taylor profile