VirtualBox 5.1.18 is an application installed on an existing host operating system; within this application, additional operating systems can be loaded and run, each with its own virtual environment. For example, several Linux distributions can be hosted on a single machine running Windows XP; likewise, XP and Vista can run on a machine running Linux, and so on. There is a free for personal or evaluation use proprietary version and a GNU General Public License (GPL) version.

Changes in 5.1.18:
This is a maintenance release. The following items were fixed and/or added:
Shared Folders: fixed case insensitive filename access (5.1.16 regression; Windows guests only; bug #16549)
Shared Folders: fixed access to long pathes (5.1.16 regression; Windows guests only; bugs #14651, #16564)
API: fixed snapshot handling of medium attachments and PCI device attachments (bug #16545)
API: make 32-bit Windows guests in raw mode boot again if the ICH9 chipset is used (5.1.16 regression)
VBoxBugReport: fixed VM log collection issue
Linux hosts: fixed autostart service script (bug #14955)
Windows Additions: fixed automatic logins for Windows Vista and newer (5.1.4 regression; bug #15904)