There's a lot of buzz around containers these days. I used to be a big fan of FreeBSD jails for many of the reasons that people are fond of containers. But there's something much better than jails: SmartOS.
SmartOS is an Illumos distribution maintained by Joyent that comes with a wealth of wonderful technologies like: KVM, ZFS, Dtrace, and the latest miracle -- LX Brands.
SmartOS is a hypervisor whose purpose is to be the substrate for cloud infrastructure. You have Solaris zones (like FreeBSD jails), but they're mapped to their own ZFS datasets. You get software-defined networking and your performance is pretty much bare metal. It's great.
For those things that don't play nicely on Solaris you can do KVM, which runs everything from Linux, OpenBSD, to Windows. You get the performance penalty of a true VM but you can do whatever the hell you want.
But... what you probably really want to do is use an LX Brand. The LX Brand is essentially a translation table that allows Linux systems calls to work on Solaris. The end result is the guest OS thinks it's Linux but it's actually Solaris. The whole userland basically works like the Linux distro and it doesn't know it's being duped. It runs basically at bare-metal speed. You get your Ubuntu running on ZFS with Dtrace. It works amazingly well and is probably the craziest black magic in tech that I've seen in a long time. Watch this video and prepare to have your mind blown.
Joyent is building their Docker infrastructure on this LX Brand and I'm super excited to try it out for my next big project. Meanwhile this site and most of my infrastructure is chugging along in SmartOS zones on my own dedicated SmartOS server, which really, if you're a competent sysadmin, are a joy in and of themselves.
I've become a bit of a fanboy but I think it's warranted. Check out SmartOS. You'll be amazed.