Sun has acquired an open source desktop virtualization vendor called Innotek, which makes software targeted at developers who want to build, test and run applications on multiple operating systems.

The Innotek product VirtualBox “enables desktop or laptop PCs running the Windows, Linux, Mac or Solaris operating systems to run multiple, different operating systems side-by-side, switching between them with just a click of the mouse,” Sun officials stated in a press release. “This allows software developers to more easily build multi-tier or cross-platform applications, or power-users to take advantage of applications that may not be available for their base operating system of choice.”

Sun acquired the small German company in a stock purchase, but did not disclose the terms of the deal as it “is not material to Sun’s earnings per share,” the company said. The transaction is expected to close in the third quarter of this year. The announcement comes just a month after Sun agreed to pay $1 billion to buy the MySQL database company, another open source vendor.

VirtualBox will remain free of charge under Sun and be placed in the company’s xVM portfolio of virtualization products, Steve Wilson, Sun's vice president of xVM, wrote in a blog posting.

“If we're going to continue to give it away, why is Sun investing in VirtualBox? In short, because the developers that build applications have a huge amount of influence on how they're deployed,” Wilson wrote in his blog. “We believe that developers using VirtualBox can help guide their friends in the data center towards xVM Server as the preferred deployment engine. Beyond that, I think there is a huge opportunity to link with Sun's other developer-related assets like NetBeans, Glassfish and (soon) MySQL. Imagine the virtual software appliances we can create using these assets, and developers will be able to start using them instantly, making it way easier to install and configure these things.”

Innotek’s VirtualBox has been downloaded more than 4 million times since January 2007, according to Sun.

For Sun, the acquisition fills a gap in its virtualization portfolio. Sun already had xVM Server to compete with VMware’s ESX Server, but with VirtualBox Sun now has something to compete against VMware Fusion or the desktop virtualization products from Parallels, Wilson wrote.