If you are concerned with having many windows open when running several virtual machines on your Windows server or workstation, then have them run headless using VirtualBox commandline tools. Additionally, you can manage these VM's using RDP (Mircrosoft Terminal Server Connection - mstsc.exe) or SSH access (if enabled)
- Download the latest version and install of [Oracle VirtualBox] [vbox]
- Download the [VirtualBox Extension Pack] [vbox] and install for the same version