How could I list all virtual machines under Virtual Box?

How can I list all VirtualBox virtual machines, including those created by other users?

By default, the VBoxManage list vms command lists the VMs owned by the current user. But what if there are many VMs, created by different users? I would like to run a VM created by another user, but cannot find any, even though I know it exists somewhere.

VirtualBox stores its data in your user profile directory - there's no "global virtualbox database" for the machine. You would have to get access to the virtualbox directory under the other user's profile.