Today docker released a beta version for Mac and Windows users, and docker is not using virtual box and the virtual-box hosted docker-machine anymore
https://blog.docker.com/2016/03/docker-for-mac-windows-beta/
The Docker engine is running in an Alpine Linux distribution on top of an xhyve Virtual Machine on Mac OS X or on a Hyper-V VM on Windows, and that VM is managed by the Docker application. You don’t need docker-machine to run Docker for Mac and Windows.
For Mac OSX, docker is using the https://github.com/mist64/xhyve, which is built on top of hypervisor framework introduced in OS X v10.10
https://developer.apple.com/library/mac/releasenotes/MacOSX/WhatsNewInOSX/Articles/MacOSX10_10.html
Hypervisor (Hypervisor.framework). The Hypervisor framework allows virtualization vendors to build virtualization solutions on top of OS X without needing to deploy third-party kernel extensions (KEXTs). Included is a lightweight hypervisor that enables virtualization of the host CPUs.