Virtualisation can de done in FreeBSD with Jails. FreeBSD Jails are great to assign certain services to little ‘virtual servers’ that are fast and light weight to use.
There are also Xen Dom0 and BHye buty they are at different stages of development. Let’s not forget about VirtualBox either.
Syscfonfig blog has a post on FreeBSD VirtualBSD and how much it has matured over the last few years. Carsten has also set up a wiki detailing all the steps needed to get VirtualBox to run on FreeBSD. It has more details than the FreeBSD Handbook VirtualBox Chapter.