Oracle VM VirtualBox is an industrial-strength open source virtualisation tool that makes it easy to create virtual machines (VMs), simulated computers that run on your PC but act as though they were separate systems. It's a powerful capability that has many different applications.
If you'd like a closer look at Windows 10 before you upgrade, for instance, then you could install Microsoft's latest in a VM, then access it in a window on your XP or Vista desktop.
Or maybe you've upgraded to Windows 10 and find a favourite old app doesn't work any more? Create a Windows XP VM and you might be able to run it again.
VirtualBox can also be a useful security tool: if you download and test apps in a VM, then any malware you might encounter will be isolated from your main system.
And it's the perfect choice if you want to try out another operating system with the minimum of hassle. Right now you can install Google Chrome OS, all the mainstream Linux variants (2.4 and 2.6), OpenBSD, OS/2, ReactOS, SkyOS, DOS, and just about every version of Windows there's ever been. (Of course you'll need to have the system discs to hand.)
VirtualBox 4 included an interface redesign, making it easier to view and manage your virtual machines. VM displays can now be scaled, so you can reduce a window size by half (for instance) and still see everything that's going on. The ability to limit a VM's CPU and IO time means the program will be less of a drain on your system's resources, and there are a host of other performance optimisations and bug fixes available.
What's new in VirtualBox 6.0.4 (see changelog for more)?
Virtualization core: support Shanghai/Zhaoxin CPUs.
User interface: handle command line arguments to VirtualBox correctly (bugs #18206 and #18197)
User interface: improvements to machine manager window, virtual optical disk creator, storage selector window and log viewer window
User interface: various small fixes and improvements
Audio: implemented time scheduling for the AC'97 device emulation to keep audio and video in sync
Graphics: basic support for VMSVGA graphics device in virtual machines using EFI
Network: fix occasional NATNet crashes (bug #13899)
Network: worked around problems in certain PCnet drivers on old operating systems
Serial: fixed connecting to pseudo terminals on POSIX hosts (6.0.0 regression; bug #18319)
Linux hosts and guests: fix for building kernel modules against Linux 5.0. Thank you Kyle Laker