Triton Data Center
github.com
github.com
They like it enough that they bought this business from Samsung, who previously developed and supported it through their subsidiary, Joyent. I worked for Joyent for a few years but left before the transition to mnx.
Triton uses SmartOS as the operating system on compute nodes. Familiarity with Solaris/illumos is helpful at that layer. If you are Using it to run Linux VMs, the amount of Solaris wizardry needed should be minimal.