Some of the features of VirtualBox are:
- Modularity. VirtualBox has an extremely modular design with well-defined internal programming interfaces and a client/server design. This makes it easy to control it from several interfaces at once: for example, you can start a virtual machine in a typical virtual machine GUI and then control that machine from the command line, or possibly remotely. VirtualBox also comes with a full Software Development Kit: even though it is Open Source Software, you don't have to hack the source to write a new interface for VirtualBox.
- Virtual machine descriptions in XML. The configuration settings of virtual machines are stored entirely in XML and are independent of the local machines. Virtual machine definitions can therefore easily be ported to other computers.
- Guest Additions for Windows and Linux. VirtualBox has special software that can be installed inside Windows and Linux virtual machines to improve performance and make integration much more seamless. Among the features provided by these Guest Additions are mouse pointer integration and arbitrary screen solutions (e.g. by resizing the guest window).
- Shared folders. Like many other virtualization solutions, for easy data exchange between hosts and guests, VirtualBox allows for declaring certain host directories as "shared folders", which can then be accessed from within virtual machines.

VirtualBox 4.0.2 (Released 2011-01-18)

This is a maintenance release. The following items were fixed and/or added:
GUI: don't crash if a removable host drive referenced from the VM settings vanished
GUI: fixed a crash when using the KDE4 Oxygen theme and clicked on the settings button (4.0 regression; bug #7875)
GUI: properly warn if the machine folder cannot be created (bug #8031)
GUI: several fixes for multimonitor X11 guests
ExtPack: don’t make the installer helper application suid root (Linux .deb/.rpm packages only)
ExtPack: improved user experience on Vista / Windows 7 when installing an extension pack
ExtPack: fixed issue with non-ascii characters in the path name during installing an extension pack (bug #7917)
ExtPack: fixed SELinux issues on 32-bit Linux hosts
VBoxManage: Host-only interface creation and removal is now supported for all platforms except Solaris (bug #7741)
VBoxManage: fixed segmentation fault when removing non-existent host-only interface
Storage: fixed possible crashes with VMDK/VHD images with snapshots and async I/O (4.0 regression)
Storage: don’t eject the physical medium if a DVD/CDROM/oppy drive is detached from a VM (bug #5825)
Storage: be more robust when a faulty guest sends ATA commands to an ATAPI device (bug #6597)
Parallels: fixed deletion of the image during suspend, pause or power off (4.0 regression)
Bridged networking: fixed host kernel panic when bridging to devices with no TX queue (4.0 regression; Linux hosts only; bug #7908)
NAT: port-forwarding rule registration respects protocol parameter (bug #8094)
E1000: fixed PXE boot issues with WDS (bug #6330)
Virtio-net: fixed the issue with TX performance in some Linux guests
ICH9: fixed VM crash (software virtualization only; bug #7885)
VGA: fixed VESA screen issue (4.0 regression; bug #7986)
Shared Folders: fixed parameter parsing when creating symbolic links, fixes 32-bit/64-bit bitness issue (bug #818)
Main: fixed crash under rare circumstances due to an invalid logging string (4.0 regression)
Main: improve error information propagation for errors preventing a VM start
Main: fixed problems with snapshots and non-ASCII characters in machine paths (bug #8024)
Webservice: now listens to localhost by default as documented (bug #6067)
Settings: do not fail loading machine settings if removeable drive attachment (host drive or image) cannot be found; with 4.0 this is much more likely when machines are moved from one host to another
Settings: fixed issue that changing a snapshot name or description was not saved to machine XML
OVF/OVA: fixed import of files created by other OVF tools (bug #7983)
rdesktop-vrdp: fix a crash during USB device enumeration (bug #7981)
Linux hosts: fixed a crash during USB device enumeration.
Linux hosts: try a bit harder to allocate memory (bug #8035; 4.0 regression)
Guest Additions: fixed parsing of parameters for guest control in VBoxService (4.0 regression; bug #8010)
Windows Guest Additions: automatic logon on Windows Vista/Windows 7 now supports unlocking previously locked workstations