Redmond’s revealed that it’s built something called Azure Cloud Switch (ACS), describing it as “a cross-platform modular operating system for data center networking built on Linux” and “our foray into building our own software for running network devices like switches.”

Satya Nadella’s Microsoft is a very different animal, unafraid to use any technology if it gets the job done. But Microsoft building a Linux? Wow. Just wow. —Microsoft has developed its own Linux. Repeat. Microsoft has developed its own Linux • The Register