VirtualBox is a free virtual machine for Windows, Mac, Linux and Solaris. VirtualBox runs the disk images without the need for drive partitioning and difficult installation. The disk images can be placed on the computer's hard drive, SSD, flash drives, or other external drives. Placing the files on an external drive allows the disk image to be taken with the user and run on any computer that has VirtualBox installed.
VirtualBox can run different operating systems on the same computer. Many of the operating systems can be downloaded for free and are legal. By downloading the VirtualBox disk image for an operating system, VirtualBox can run that operating system without having to install the operating system.
Virtual Box Disk Images Downloads
www.OSBoxes.org
www.VirtualBoxes.org
sourceforge.net/projects/virtualboximage/files (Not updated in years, but they may have something you are looking for)
VirtualBox Free Download
www.VirtualBox.org
A combined list of operating systems for download at the three sites shown above (there may be more OSes than listed):
Absolute
Android
Antergos
antiX
Arch Linux
Aros
BackBox
BackTrack
Bio-Linux
Black Lab
BLAG
Bodhi
CAINE Linux
Calculate Linux
CentOS
ClarkConnect
CrunchBang
Cub Linux (Chromixium)
Debian
Debris Linux
Deepin
Devuan
Dream Studio
Dreamlinux
EasyPeasy
Elementary OS
Excelixis
Fedora
Feren OS
Foresight
FreeBSD
FreeDOS
Freezy
Fuduntu
Gentoo
gNewSense
gOS
Granular
Haiku
HandyLinux
IPFire
Kali Linux
KaOS Linux
KDE Neon
Korora
Kubuntu
Linguas OS
Linpus
Lite Linux
Lubuntu
LXLE
Mageia
Makulu
Mandriva One
Manjaro
MEPIS
MidiFlux
Minix
Mint Debian
Mint Linux
Monomaxos
MoonOS
Nexenta
Nitrux
OpenGEU
OpenSolaris
OpenSUSE
OzOs
Parrot Security OS
PC/OS
PCLinuxOS
PearOS
Peppermint
Phoenix
Pinguy
Plan 9
Point Linux
Progex
Puppy
Q4OS
Qimo4Kids
ReactOS
Remix OS
RoboLinux
Sabayon
SalineOS
Scientific Linux
Shift Linux
Slackware
SliTaz
SnowLinux
Solus OS
SparkyLinux
SuperX OS
Syllable
Tanglu
TinyMe
Trisquel
TrueOS
Ubuntu
Ubuntu Gnome
Ubuntu Mate
Ubuntu Server
Ubuntu Studio
Ubuntu Studio Ultimate
Ubuntulite
Ulteo
Unity
VectorLinux
Vixta
Wolvix
Workbench
Xubuntu
Zentyal
Zenwalk
Zonbu
Zorin OS