The Nomad is a heavy gunship of unknown make and model, looted by Sarah Skamrev ("Modem") from its previous pirate owner. It is unusual for its general type, both in that it is considerably larger than most gunships, capable of interplanetary travel, and in having sufficient aerodynamic properties that a loss of power to its eezo core would not render it impossible to fly.
The Nomad, when acquired, was fitted with a Helios ion drive and SDR "mini" drive core, multi-launch modular missile bays, dual automatic cannons (limited fire arcs), and two antipersonnel machine gun mounts. Modem upgraded it with a more flexible missile system and improved the original drive power, and added amenities such as a small kitchen, workshop, and bunk space, making the Nomad suitable to live up to its name as her wandering home. For comparison to other gunships, if one were to remove the additions made by Modem, you could just barely fit a M-35 Mako in the rear bay.
In theory, the Nomad could support a frigate-grade cannon, but the framework necessary to mount such a weapon would render it all but impossible to aim other than along the ship's axis, and would make conventional landing impossible. Modem often loads the missile bays with Tornado Swarm missiles or Harpoon interceptors.
The appearance of the Nomad is actually that of the Striga heavy omnifighter from Battletech.