There is only a partial version for x86 while amd64 remains a platform to be ported to on FreeBSD.
You can't build any version later than 2.0.0 because they need kBuild>1.4.x and that is the only patched version for FreeBSD.
Sun could use some help and could try openly asking the BSD community on forums, blogs,and other resources again
instead of waiting for volunteers. The kBuild above was patched not because they asked but because one BSD member asked another BSD member about the problem.
Like KVM, kqemu, and Xen, it is still a front end to qemu. I wish it did have full qemu functionality built in, that would be nice.
Another problem is that it requires 32bit libraries to work. Don't believe me? Try installing it on any 64bit Windows or Linux box without ia32libs/32bit libs.
It hasn't been completely ported to Windows- you need mingw to build, qt3/4 libs, alsa, pulse, etc. None of these are available as exe files AFAIK.
Better put VirtualBox in the catagory with Xen, KVM, and VirtualIron- a work to port FreeBSD to in the future.
If you think about it, the only "true" virtualization software that allows you to directly use hardware are live images. You can even execute binaries from the host system by simply mounting in most cases.
I'm not a kernel hacker so you're more than welcome to join me in trying to port.