VirtualBox

What is Sun VirtualBox
VirtualBox is an x86 virtualization software package, originally created by German software company innotek, now developed by Oracle as part of its xVM virtualization platform. It is installed on an existing host operating system; within this application, additional operating systems, each known as a Guest OS, can be loaded and run, each with its own virtual environment.

Homepage Link: http://www.virtualbox.org/

Host or Guest
OS/2 and eComStation can act both as a host operating system or as a guest operating system when running VirtualBox. Some constraints apply to what you can do and specifically HOW you do things depending on the availability and combinations of "hosts" and "guests":

In this case, OS/2 or eCS is your machines operating system. By installing VirtualBox for OS/2 and eComStation, you will be able to run different operating systems as "virtual machines" on your PC.
 * ...as a Host OS

Running OS/2 or eCS as a guest means that your PC is actually running some other operating system (like Linux, Windows, ...) and OS/2 or eCS will be available as virtual machines.
 * ...as a Guest OS

VirtualBox for OS/2 and eComStation
This software is needed if you want to run different operating systems from within your OS/2 or eComStation PC (it will thus give you a VirtualBox 'host' on your machine). Whereas, if you intend to run OS/2 or eComStation as a virtual machine on a different operating system environment (e.g. "run OS/2 on a Windows machine"), you will need to download the appropriate VirtualBox version (in this case the Windows version).

Different ports of VirtualBox for OS/2 and eComStation are available for free download:

Version 1.x.x-r9190 (20080531) from Paul Smedley's Homepage
 * Paul Smedley's port:

Version 1.6.1-r9201 (20080604) from an anonymous FTP server
 * T.Ebisawa's port (contains patches to fix DBCS-compliant problems):

References & Links

 * VirtualBox Official Site
 * Installing Windows on VirtualBox Tutorial