How is this different from Azure Container Service?

I’m not sure if I’m missing something, but Azure has a container service already (ACS) which can spin up clusters running Swarm, Mesos and Kubernetes. What is the difference between that and Docker for Azure?

Docker for Azure is built and maintained by Docker Inc. You can read more about our motivations for building Docker for Azure here:

As of today, using Azure Container Services (when using swarm as the orchestrator) does not support swarm mode (a.k.a - Docker 1.12 and up). Deploying the template from the “Docker for Azure” link in the docker docs will support swarm mode.

Docker Swarm mode has to be initialized and is very much supported.