Dockersocat serves the Docker socket (/var/run/docker.sock) on a TCP port, default 2375.
If you're already running a Docker container and want to be able to access the Docker socket from within the container, you normally need to stop the container, perform some Docker wizardry to add /var/run/docker.sock as a mount, and restart the container.
Dockersocat is more convenient.
Dockersocat exposes /var/run/docker.sock on a TCP port your container can access.
brew install 4d63/dockersocat/dockersocat
On the host:
dockersocat
From within a container:
DOCKER_HOST=host.docker.internal:2375 docker ps
Use this at your own risk. The Docker for Mac release intentionally does not expose the Docker API on a TCP port for security reasons. Any application on your computer, including containers running within Docker for Mac, will be able to control Docker and therefore mount, access, and modify any folders that Docker can access, and do so as root. Other bad things could happen that aren't documented here.