VMware is buying privately held SpringSource, the San Mateo, California, outfit behind the open source Spring Framework for Java application development, a totally new direction for VMware having nothing at all to do with virtualization - at least not on the surface.

The acquisition will give it an application platform that can be used to build, run and manage applications on both internal and external cloud architectures.

It's supposed to make VMware more familiar with applications, particularly apps that haven't been written yet, which CEO Paul Maritz said would contribute significantly to its growth by making the cloud simpler to operate.

Maritz insisted during a conference call Monday that the acquisition was all about "innovation" and would transform VMware, pushing it out beyond the hypervisor and the operating system since apps are increasingly written to frameworks, not operating systems.

VMware's paying roughly $362 million in cash and stock. It will assume about $58 million in unvested stock and options and there's a $60 million retention pool good over four years, making the SpringSource purchase worth about $422 million, one of the largest open source acquisitions so far.

It's also VMware's biggest acquisition to date and will put a 100 basis point squeeze on its non-GAAP earnings for at least the next couple of quarters, which may be why its stock dropped after-hours Monday.

VMware expects the 150-man SpringSource, which peddles the usual open source subscriptions and support, to turn cash flow positive in the first half.

VMware was not prepared to talk about the acquisition's revenue run rates, growth rates or integration details but did reaffirm its own guidance.

The deal has already been okayed by SpringSource stockholders and should close by the end of September.

VMware said it plans to continue to support SpringSource's open source model and the interoperability of its software with various other middleware.

In a canned statement ahead of a conference call Maritz said, "Today's modern computing environments are moving to an application and data-centric world powered by state-of-the-art virtualized and cloud computing platforms. The combination of SpringSource and VMware capitalizes on this shift and places us right at the intersection of the most important forces in the software market today - virtualization, modern application frameworks and cloud computing."

The companies are supposed to develop integrated Platform-as-a-Service (PaaS) solutions that can be hosted at customer data centers or at cloud service providers.

VMware says the widgetry should let users quickly build new enterprise and web applications and run and manage them on the same VMware vSphere-based internal or external clouds that can also host and manage their existing applications, providing an evolutionary path to the future.

It quoted Forrester Research's forecast last month that the PaaS market will be worth $15 billion by 2016.

SpringSource is already reportedly used by most of the Global 2000. Maritz said there was overlap in the customer base.

SpringSource users include JP Morgan, Orbitz, Accenture and Cap Gemini.

SpringSource is a devotee of so-called "lean software," meaning widgetry that cuts cost and complexity, increases productivity and accelerates the delivery of high-quality business-critical applications.

Its business revolves around supporting the Spring Framework, the prominent enterprise Java programming model used by two million developers worldwide by Gartner's count; Apache Tomcat, the popular Java app server; Groovy and Grails, the rapidly growing dynamic language and web application framework each with more than 70,000 downloads a month nowadays; and the bought-in Hyperic application monitoring and management tools, said to have 3,500 deployments worldwide.

VMware has been getting cozy with SpringSource for the last nine months and put a couple of million dollars in the company in April.

SpringSource got at least $25 million in VC funding from Accel Partners and Benchmark Capital over the years.