Similar to the now-rather-defunct Debian GNU/kFreeBSD that paired the Debian GNU user-space with the FreeBSD kernel rather than the Linux kernel, developers have done the same with Ubuntu and called it UbuntuBSD. This first UbuntuBSD beta release is based off Ubuntu 15.10 Wily Werewolf and the FreeBSD 10.1 kernel.
This Ubuntu+FreeBSD operating system ships with the Xfce desktop, is designed for both servers and desktops, and offers complete ZFS file-system support.
I have yet to try out UbuntuBSD, but if you want to learn more, visit their SourceForge project site. Hopefully this project will be more fruitful than the other attempts like Debian GNU/kFreeBSD, Arch BSD, Gentoo/BSD, etc.