Nomen

"Compared to our code of noninvolvement, your Prime Directive is practically an incitement to riot."

Practically nothing is known about the Nomen. They were only recently discovered when the FoS colony in Azara noted strange readings on a newly installed deep-space scanner. A previously undiscovered xeno station was anchored in one of the asteroid belts of the system and found purely by chance, emitting only the tiniest amount more radiation than would otherwise be expected of background radiation in space.

When investigated more closely, the station seemed to "pack and leave", sending in multiple Federation languages it's apologies before disappearing off sensors.

It is unknown where or how the Nomen operate.

[Addendum]

The crew has found a Nomen embassy on the Istrid homeworld, and the representatives there seem reasonable, if guarded.