VirtualBox for Mac is a freeware virtualization software alternative to Parallels Desktop and VMWare Fusion for Mac OSX operating systems. This version is still in Beta and runs only on Intel based Macs. It allows you to use Windows Vista or any flavour of Linux as the guest OS.

VirtualBox offers regular virtualization application features such as:

-Network adapter, sound adapter and video display adapter drivers for guest OS
-Share folders on Mac host with Windows/Linux guest: These would appear as virtual drives inside the guest virtual machine
-RDP protocol over USB
-CD/DVD ROM, Flobby drives
-USB controller driver
-Additions for Windows and Linux; for improved video and USB performance and integration of the mouse between the Mac host and the guest virtual machine.

While VirtualBox cannot be a complete replacement for Fusion or Parallels (for e.g. Direct X 3D gaming support is absent), it is definitely a worthy freeware virtualization solution for Mac.

To build VirtualBox on Mac, follow instructions on the software wiki. Download VirtualBox for Mac Intel here. VirtualBox for Windows has previously been covered here.