VirtualBox is ridiculously simple to set up and get virtual machines going. Shared folders, shared clipboard and much more are no issue.
But.
It eats resources. The installed virtual machines (VM) run relatively slow. What have you found to be feature comparable - and most importantly more resource-efficient - alternatives for running VMs under Linux?
Without any kind of software behind GUI this is almost useless and I think that CLI (or even TUI) are today so underrated that we should give more and more power to them instead of GUI