Mesosphere Datacenter system is a new OS that spans all of the machines in the data-center/cloud. Applications, services and data can be deployed - highly scalable, and elastic. Recently Microsoft is teaming with Mesosphere (it is rumored to be bought out by MSFT) to get added value from Microsoft Azure using Mesosphere Meso DCOS by porting Apache Meso for Windows Servers and at the same time catering to Linux.
You can run Meso DCOS on Microsoft Azure. It is free on Microsoft Azure (https://mesosphere.com/azure) but requires a bit of information about yourself at this link (https://mesosphere.com/azure). You can also sign-up for early access at the same link.
It will be available soon for Google Cloud Platform and it is already available on Amazon Web Services with the free community edition. Get started free on Amazon here.
Apache Meso (Open source) is not the same as Mesosphere Meso but watch this well rounded video on Apache Mesos by Benjamin Hindman to get a feeling for working with DCOS: "Building and Running Distributed Systems using Apache Mesos"
Introducing the Mesosphere Datacenter Operating System (DCOS) from Mesosphere site.