Source code for Solaris zones is indeed available; but I wouldn't consider it widely deployed.
Why would you not consider it widely deployed? If it needs to be said: just because you don't use something doesn't mean that others aren't. Speaking only for us (I work for Joyent), we have deployed hundreds of thousands of zones into production over the years -- and Joyent was running with FreeBSD jails before that. And that's just us; there are many others in the illumos/SmartOS/OmniOS, Solaris and FreeBSD communities who have been running this technology in production -- broadly -- for years. Perhaps OS virtualization is a new technology for you, but understand that it's not new for everyone; some of us have been doing this for a while -- widely deployed and in production.
I wouldn't consider it "widely deployed" compared to the Linux installed base.
Sure, Joyent (and others) has "deployed hundreds of thousands of zones into production over the years", but you guys are the only well-known, large-scale, public hosting service using zones (and you're damn good at that, no doubt about it!)
Now compare with dotCloud, Heroku, Dreamhost, 1&1, Mediatemple, OVH, Amen (just to name those I can remember without doing an extensive research): those guys have also "deployed hundreds of thousands of Linux-based VPS into production", using VServer, OpenVZ, and more recently, LXC.
Don't get me wrong: I'm a big fan of Solaris (and its heritage); I have lots of my marbles on ZFS; I hacked basic ZFS support in Docker just for fun a while ago; and if I knew better, I would love to find a way to run sub-zones and a ZFS pool in a Joyent SmartOS instance and port Docker to your platform. But there is a helluva lot of Linux hosters out there.
I'll close with a lovely paraphrase: « Perhaps LXC containers are a new technology for you, but understand that it's not new for everyone; some of us have been doing this for a while â widely deployed and in production. » ☺
Just because popular hosting companies are not using Solaris zones, that does not mean there are not large Zones-based deployments elsewhere in the industry. Particularly, some major corporations (including banks and telcos) are using Zones in their production Solaris environments. These turn out to be particularly large deployments, with hundreds of machines in data centers across the US.
These users do not broadcast their use of Zones, but having worked with them, they certainly do exist.
*Used to work at Sun on a project related to Zones and ZFS.
> Perhaps OS virtualization is a new technology for you [...] some of us have been doing this for a while
Your comment makes a fair point, but it's really diminished by your condescending tone.