I wouldn't quite go as far as to call Borg a PaaS. It's at a somewhat lower level, closer to IaaS. You get a known quantity from it in the form of a stable, tun

I wouldn't quite go as far as to call Borg a PaaS. It's at a somewhat lower level, closer to IaaS. You get a known quantity from it in the form of a stable, tuned, stripped down underlying Linux image, plus a relatively small set of services, but you can deploy pretty much whatever the hell you want without a lot of constraints a "true" PaaS would force you to accept.