SmartOS by Nahum Shalman
From the description of the April 2013 BBLISA meeting at http://www.standalone-sysadmin.com/bl...
Nahum Shalman gave a really nice introduction to SmartOS, a derivative of OpenSolaris which is maintained by Joyent. Interestingly, the Linux-native KVM was ported to the SmartOS kernel, allowing creative and secure uses of jails and virtual sandboxes, all taking advantage of native ZFS, dtrace, and all kinds of delicious Solaris-y goodness.