VirtualBox is virtualization software that allows you to create self-contained virtual machines (VM). It’s actually open source, and the only one current virtualization software that is full open source (and free!). There is a Mac OS X version and it supports older versions of Windows (Windows NT4, 2000) as well as the latest (Windows 7), in addition to DOS, Linux, Solaris, OS/2, and other guest operating systems.

With version 4.1.2, there isn’t much that is specific to Mac OS X hosts, but it’s still a recommended upgrade.

Changes
* VMM: fixed handling of the sysenter/sysexit machine instructions in 64-bit guests on Intel hosts
* GUI: added linked clone support
* GUI: fixed error check when changing the VM controller settings (4.1.0 regression; bug #9246)
* GUI: fixed the inclusion of additional information (license, vendor, …) on OVF export
* GUI: when taking a snapshot from the VM selector, don’t do a live snapshot
* GUI: fixed immediate crash during start on certain environments due to a library version conflict
* Guest control execution: implemented copying single files from guest to the host (directories and filters not supported yet)
* Guest control execution: limited to serve up to 5 guest processes at a time by default
* Main: return the correct RDP default port fixing settings warnings in the GUI if the remote display was enabled at runtime (bug #9368)
* VBoxSVC: made the path comparison OS independent when images are registered (bug #9303)
* VBoxSVC: several fixes/performance improvements for cloning of VMs
* Snapshots: fixed “Solid-State drive” flag survival on snapshot creation (bug #9379)
* VBoxManage: implemented copyfrom and stat guest control tools to copy files from guest to host and to check for existence of files on the guest
* VBoxManage: fixed extpack install –replace (bug #9308)
* VBoxManage: allow to start multiple VMs with startvm
* VBoxManage: experimental support for SATA CD/DVD hotplugging
* VRDP: fixed a case when the screen was not redrawn correctly (bug #9242)
* USB: fixed issues with remote filters being applied to local USB devices
* OVA: fixed import of renamed OVA files (bug #9033)
* Guest Additions: keep logged in user count in out-of-memory situations and warn about it

Download: Downloads (VirtualBox.org)

Oracle VM VirtualBox (the full title) is virtualization software for x86 platforms (Intel/AMD) and allows you to run various Guest OSes under Mac OS X, Windows, Linux, and other host operating systems. It is similar in functionality to Parallels Desktop and VMWare Fusion as far as Mac OS X users are concerned. There is a limited functionality when it comes to running Mac OS X guest sessions, although a Mac as the host machine is required.

It’s being listed as a maintenance release, with no new main features or additions.

Mac OS X related Changes
* Mac OS X hosts: fixed incompatibility with recent Mac OS X versions in 64-bit mode
* Mac OS X hosts: fixed incompatibility with hosts with more than 16 cores
* Mac OS X hosts: fixed painting corruptions on a second monitor in 64-bit mode
* GUI: restored functionality to set an empty host key to disallow any host key combination (4.0.6 regression)
* VBoxManage: added controlvm screenshotpng subcommand for saving the screenshot of a running VM in PNG format
* NAT: built-in services use the correct Ethernet addresses in Ethernet header and in ARP requests
* Host-only networking: fixed adapter reference counting
* E1000: fixed rare guest crashes with Linux SMP guests
* SATA: fixed guest disk corruption under rare circumstances (only relevant for guests with more than 2GB RAM)
* Storage: fixed data corruption after a snapshot was taken with asynchronous I/O enabled
* Floppy: several improvement
* HPET: another fix for time jumps
* 3D support: fixed a potential crash when resizing the guest window
* Snapshots: fixed another bug which could lose entries in the media registry when restoring a snapshot
* Shared Folders: don’t stop mounting the other valid folders if one host folder is inaccessible
* Guest Additions: fixed inappropriate Guest Additions update notification when using vendor-specific version suffixes

Links
* Downloads (VirtualBox.org)
* Full Changelog (VirtualBox.org)

VirtualBox is a free/open-source Virtualization solution for Mac OS X running on Intel-based Macs. In addition it can be used on Windows-based and Linux-based machines.

Innotek VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL).

Presently, VirtualBox runs on Windows, Linux and Macintosh hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista), DOS/Windows 3.x, Linux (2.4 and 2.6), and OpenBSD.

VirtualBox is being actively developed with frequent releases and has an ever growing list of features, supported guest operating systems and platforms it runs on. VirtualBox is a community effort backed by a dedicated company: everyone is encouraged to contribute while innotek ensures the product always meets professional quality criteria.