Sun has announced plans to acquire desktop virtualisation vendor Innotek, as part of an ongoing effort to woo developers to support its own Sun xVM platform.

Stuttgart, Germany-based Innotek, which was founded in 1992, is best known for an open-source virtualisation tool called VirtualBox. It first made VirtualBox available in January of last year. According to Sun, the software has been downloaded more than 4 million times since then.

Steve Wilson, who heads Sun's xVM team, said in his blog Tuesday that the company hopes the "super slick" VirtualBox technology will help broaden interest among developers in the xVM product line, which Sun announced last fall.

Sun officials think that developers writing applications for VirtualBox "can help guide their friends in the data center toward xVM Server as the preferred deployment engine" for the apps, Wilson wrote.

The two technologies offer some of the same capabilities, he acknowledged. But he said that xVM Server is a "bare-metal hypervisor" that gets installed directly on hardware, not on top of an existing operating system. In contrast, Wilson added, VirtualBox is a lightweight app that runs on top of an operating system and lacks the datacentre features of xVM Server, such as support for live migration of data.

VirtualBox supports Windows, Linux, Macintosh and Solaris hosts. Just Monday, Innotek announced the first beta release of the virtualisation software for OpenSolaris, the open-source version of Sun's Unix operating system. And last Wednesday, it released an updated beta-test version of VirtualBox for Mac OS X.

The cross-platform support "makes VirtualBox a software developer's dream," Wilson wrote in his blog post. "You can easily set up multiple virtual machines to develop and test your multi-tier or cross-platform applications - all on a single box."

Sun didn't disclose the purchase price that it's paying for Innotek, which is privately held. But the company said that the acquisition, which is due to be completed by the end of next month, won't have a material effect on its short-term earnings.

One thing Sun does plan to do is to continue making VirtualBox freely available to users. Sun's open-source strategy is based on its belief that such offerings can win support from developers, which in turn will help broaden the market for the company's hardware and its tech support services.

This is the second open-source acquisition deal signed by Sun within the past few weeks. Last month, the company said it would pay $1 billion to buy open-source database vendor MySQL.