This is an alternate mirage network device to use when building unikerels in unix.
Inside mirage-net-unix, a network device is created by opening a tap device, whereas in mirage-net-psock, by calling sockets API and opening a raw socket, one would get a network device directly sending to/receving from a network interface.
For the obvious, if you want to access traffic directly from network interfaces. It's possbile to do the same with standard mirage-net-unix, however, usually it involves extra local host network configuration: setting up linux bridges, connecting interfaces, and probably setting up NAT rules using iptables utilities. But with mirage-net-psock, calling connect with the intended interface name in your code will just do you the same. As it fulfills the ETHIF signature, you could easily build you own network stacks over it and be ready to talk to the outside world.
This tool lays the ground for me-box/core-network component, which is responsible for managing the communications between different containers within Databox. After Databox is started, containers are created/removed dynamically, so do the dedicated networks that they are attached to. core-network will always have an interface on these networks so that it could sit in the middle and control/monitor the traffic flows. mirage-net-psock facilitates the reaction to all the interface-up/-down events for core-network.