VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product 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) version 2. See "About VirtualBox" for an introduction.

Presently, VirtualBox runs on Windows, Linux, Macintosh, and Solaris hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista, Windows 7), DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, OS/2, 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 Oracle ensures the product always meets professional quality criteria.

Changelog for VirtualBox 4.0
VirtualBox 4.0.6 (released 2011-04-21)

This is a maintenance release. The following items were fixed and/or added:

VMM: fixed incorrect handling of ballooned pages when restoring a VMM from a saved state
VMM: don't crash on hosts with more than 64 cores / hyperthreads; implemented support for up to 256 host cores (except Windows hosts; bug #8489)
VMM: fixed guru meditation for PAE guests running on hosts without PAE (bug #8006)
VMM: fixed slow Linux guests with raw mode and recent guest kernels (bug #8726)
GUI: support host key combinations (bug #979)
GUI: fixed progress indicator (bug #7814)
GUI: show the mouse pointer while the VM is paused if the USB tablet mouse emulation is used (bug #6799)
GUI: adapt the snapshot folder as well when renaming a VM (bug #8469)
GUI: persistently remember the last folders of the disk/DVD/floppy selectors
GUI: never allow to start a VM with USB-2.0 activated if the proper extension pack is missing (bug #8182)
GUI: fixed hang/crash when opening a file dialog in an non-existing folder (bug #8673)
Snapshots: fixed a bug which could lose entries in the media registry when restoring a snapshot (bug #8363)
Snapshots: allow snapshots to be stored in the VM directory
3D support: fixed a crash if a VM was forced to terminate (Windows hosts only; bug #7133)
Storage: fixed memory leak (4.0 regression; bug #7966)
Storage: fixed access to iSCSI targets over internal network
Storage: fixed reading from disks with more than one snapshot for VHD and VMDK images with disabled host cache (bug #8408)
Storage: fixed a possible hang during VM suspend after an I/O error occurred
Storage: fixed a possible hang during VM suspend / reset (bug #8276, #8294)
Storage: automatically create a diff image when attaching a streamOptimized VMDK image to a VM
ATA/SATA: fixed automounting of virtual CD/DVD mediums with recent Linux distributions by correctly reporting the current profile as 'none' if no medium is present
Buslogic: fixed emulation for certain guests (e.g. jRockit VE)
Host-Only Networking: fixed interface creation failure on Windows hosts (4.0.4 regression; bug #8362)
Host-Only & Bridged & Internal Networking: fix for processing promiscuous mode requests by VMs, defaulting to switch behaviour
Host-Only Networking: fixed connectivity issue after resuming the host from sleep (bug #3625)
Bridged Networking: support for interface bonding on Mac OS X hosts (bug #8731)
NAT: fixed processing of ARP announcements for guests with static assigned IPs (bug #8609)
VRDP: backward compatibility with VRDPAuth external authentication library (bug #8063)
Shared Folders: don't fail to start a VM if a path is not absolute, for example when importing an OVF from a different host (bug #7941)
Audio: fixed crash under certain conditions (bug #8527)
USB: fixed a crash when plugging certain USB devices (bug #8699)
HPET: fixed time jumps when reading the counter (bug #8707)
OVF/OVA: automatically adjust disk paths if the VM name is changed on import
OVF/OVA: fix export to slow medias
OVF/OVA: automatically repair inconsistent appliances with multiple disks (bug #8253)
rdesktop-vrdp: fixed an assertion triggered under certain conditions (bug #8593)
Windows hosts: fixed occasional hangs during VM shutdown because sometimes COM was not properly uninitialized
Mac OS X hosts: prevent the mouse from leaving the VM window while captured
Mac OS X hosts: keep aspect ratio while resizing in scale mode (shift for old behaviour) (part of bug #7822)
X11 hosts: fixed Yen key support (bug #8438)
X11 hosts: fixed a regression which caused Host+F1 to pop up help instead of sending Ctrl+Alt+F1
Linux hosts / Linux Additions: mangle IPRT symbols to allow installing VirtualBox inside a VM while the Guest Additions are active (bug #5686)
Linux hosts / Linux guests: workaround for a bug in GLIBC older than version 1.11 leading to crashes under certain conditions (signed/unsigned problem with memchr on 64-bit machines)
Solaris hosts: fixed a deadlock in event semaphores that could lead to unkillable VM processes
Windows Additions: fixed Sysprep parameter handling
Windows Additions: fixed spontaneous guest reboots under certain circumstances (4.0.2 regression; bugs #8406, #8429)
Windows Additions: added auto logon support for locked workstations on legacy Windows versions
Windows Additions: fixed driver bugcheck error when handling PnP messages (4.0 regression; bug #8367)
Windows Additions: fixed memory leak in VBoxVideo
X11 Additions: added support for X.Org Server 1.10 final
Linux Additions: Linux kernel 2.6.39-rc1 fixes
Linux Additions: improved auto-run support (bug #5509)
Linux Additions: fix mouse support on SUSE 11 SP 1 guests (bug #7946)
Solaris Additions: added support for X.Org Server 1.9
Guest Additions: various bugfixes for guest control execution
Webservice: use own log file, with log rotation to limit size