CEO: Randall Stephenson, appointed in 2007 after three years as AT&T's COO.

How AT&T got into cloud computing: AT&T's foray into the cloud began in 2006 with its purchase of the USinternetworking, an application service provider with enterprise customers in more than 30 countries. When announcing Synaptic in August 2008, AT&T said it had combined USi technology's five "super Internet Data Centers" in the United States, Europe and Asia, which will act as regional gateways to the AT&T cloud network.

Who uses the service: Synaptic is powering major Web properties such as the official Web site of the U.S. Olympic Committee.~~

Company name: Enomaly 

Founded: 2004

Location: Toronto

Cloud offering: Enomaly's Elastic Computing Platform (ECP) is software that integrates enterprise data centers with commercial cloud computing offerings, letting IT pros manage and govern both internal and external resources from a single console, while making it easy to move virtual machines from one data center to another.

Why we're watching it: Unlike the other nine vendors on this list, Enomaly doesn't offer services of its own over the Web. But its software could prove crucial as enterprises grapple with the problem of managing a wide array of computing resources that live both inside and outside the firewall. Intel has recognized Enomaly's promise, bankrolling the company's product development, which focuses heavily on managing the various hypervisors used both within enterprises and by cloud providers.

CEO: Richard Reiner, called out of semi-retirement to become Enomaly CEO this year. Most recently, Reiner was founder and CEO of Assurent, a software-as-a-service company acquired by Telus in 2006.

How Enomaly got its start: Enomaly was born five years ago as a consulting business, but later developed an open source management tool that runs on top of the Xen hypervisor. Enomaly dropped its consulting business for good last year to focus on cloud management software.

Who uses the service: More than two dozen customers have been named publicly, including Business Objects, France Telecom, NBC, the Canadian government, Deutsche Bank, Best Buy, and several universities.

Company name: Google 

Founded: 1998

Location: Mountain View, Calif.

Cloud offering: Google Apps, a set of online office productivity tools including e-mail, calendaring, word processing and a simple Web site creation tool; Postini, a set of e-mail and Web security services; and the Google App Engine, a platform-as-a-service offering that lets developers build applications and host them on Google's infrastructure.

Why we're watching it: No one knows the Internet quite like Google. While the company's main focus is crawling the Web and delivering advertising-supported search results, Google's foray into software-as-a-service applications for businesses is hastening the industry's move from packaged software to Web-hosted services, and App Engine provides a credible alternative in the platform-as-a-service market.