I've always wanted to know more about the Nyberrite Alliance from DS9/"The Way of the Warrior", considering Worf wanted to join it.
So far as I know, they've not even been mentioned. I would like to see them featured one day. It's a slight pet peeve of mine that new races and nations are invented in Trek books when they are so many unexplored players already established. Why invent a new organization/nation/whatever when you can use a canonical name that has little or nothing attached to it? Why couldn't the Goeg Domain, say, have been the Nyberrite Alliance? Anyway, thinking over what we know about the Nyberrite Alliance, it's a long way from Bajor even by 24th Century standards, it's always looking for well-trained spacers, and it accepts members of multiple species. We don't know if it's a government, a private mercenary force, or what.
That's one of the things I like about Christopher's novels. He often gives background aliens a name or applies a name mentioned in the show to an unnamed race, rather than creating a brand new species.
Maybe they are the 24th century version of Blackwater, the private security firm, providing military and police functions for client systems?