Watch a slideshow of these 11 open source companies.

"In the dot-com bust it was Unix to Linux migration because Linux was cheaper than Solaris on SPARC," says Barry Crist, CEO of Likewise, a maker of integration and identity management software for mixed environments. "Phase 2 [of corporate open source adoption] has been accelerated by the current economic conditions. IT is looking to do things in a cost-effective manner and there are a lot of viable open source solutions out there."

Slideshow: Top 10 Open Source Hall of Famers
Open Source Definition and Solutions

Adoption has also been fueled by the success of established open source companies such as Red Hat, Novell, Alfresco and  SugarCRM, which have proven to enterprise users that it isn't the development process but the results (and quality support) that matter.

"The license terms attached to products have become secondary to the value it offers," says Mike Olson, the CEO of Cloudera and the founder of Sleepy Cat, which he sold to Oracle in 2006 when the Berkeley DB derivative had more than 200 million deployments. "People now are much more rational about how they adopt technology across the board. Open source is a detail, not a defining characteristic. At Sleepy Cat, we were proud to be an open source company. At Cloudera, I think of us as an enterprise software company that happens to be built on open source software."

The vendor also is a member of a group of open source companies that Network World has identified as being worth watching.

Cloudera is bent on making the open source Apache project Hadoop easier to use and available to a wider audience. The powerful Hadoop technology is considered a cost-effective way to manage and store large amounts of data, and mine intelligence. Yahoo is the biggest contributor to the open source project also used by Facebook and Google.

Cloudera doesn't count that trio as customers, but the three offer proof as to the power of Hadoop.

Another cloud vendor to watch is Eucalyptus Systems. The company just released Eucalyptus Enterprise Edition, which lets users implement a cloud environment using existing network infrastructure without requiring modification.

The current edition creates a sort of proxy that makes internal virtualized environments appear to run just like Amazon Web Services including Elastic Compute Cloud (EC2) and Simple Storage Service (S3). A single management console works will multiple hypervisors including Xen, KVM, vSphere, ESX and ESXi.