Sun's free and open source virtualization software, VirtualBox, has seen several upgrades since we took a look at a beta early this year. Sun today announced a significant update to version 2.1, with several important feature additions for those running virtual machines under Mac OS X.

Since the beta, Sun has addressed nearly every issue we pointed out back in February. The latest release in particular adds support for hardware 3D graphics acceleration of OpenGL in Windows guests. Hardware virtualization support for Intel VT-x and AMD-V now works on Mac OS X, and that support enables 64-bit guest operating systems to be hosted by 32-bit operating systems as long as the hardware is 64-bit capable. Other Mac OS X-specific improvements include the addition of ACPI host power status reporting and the ability to pause running VMs when your Mac is put to sleep and resume the paused VMs on wake.

Sun has a complete list of changes, including bug fixes and other improvements, on the VirtualBox website. VirtualBox, like Parallels Desktop and VMware Fusion, only works on Intel-based Macs, and is available for download now. If your virtualization needs don't require lots of host integration, à la Coherence or Unity, or the words "free" or "open source" rub your rhubarb, then VirtualBox is certainly worth a look.