Oana as one of the few halfling organizations that promote and protect the Halfling species as a whole. They are a known secret among the halflings and a rumor among the other races. Halflings will spread rumors about mistreated halflings leaving their employer only to have the employer come across a string of bad luck.
Weather they are to be believed or not the bad luck often comes from the Oana, the secret enforcers of Halfling society. From stolen secrets to outright assassination the Oana will do everything it can to insure Halflings are treated well. While many criminal organizations have claimed to be the Oana no one is sure if they were the real Oana or if they just used the name to inspire fear and respect.
Wherever there is a large enough population of Halflings there is the Oana. Each city has an Oana that operates independently from other cells. The Oana operate in small groups called families, more often then not these are actual families that pass on these traditions and skills to their children. Usually the Gran'a or Great Mother leads a family, Oana leadership often being matriarchal.
With older or larger cities there will be more Oana families that keep int touch and while individually they are seperate groups they often look to the eldest as the wisest for their aid. These Elder Gran'a can often control on upwards of a dozen families.
Oana is just a fey take meant to scare you. Regardless it would be best not to see if it is true.
Oana has safehouses in every major city with a healthy Halfling population. Being linked to black markets, spies, and assassins the Oana has a large amount of gold, silver, and copper that they frequently use to promote Halfling communities.
A halfling must serve. This has been built into their very being and when a halfling has no one to serve they become more susceptible to any kind of coercion. When the Halflings were made by the Fey they were bred to be servants but with the Archfey long since gone from the world they needed new masters. At first they followed the first humans who found them but not all of humanity were deserving. A few Halflings rebelled and slew their unkind masters fleeing into the night.
But a halfling must serve so these rebels searched for a new way to serve and they found it within the community. These first Halfling gathered around the unlit hearth, Oana in the halfling language, and swore to make sure their people would not suffer as they had. They formed their society under the name Oana in recognition of their pact and as a symbol, they would be a place of rest but not one of comfort. For slaying their new masters the Oana was banished from society, the other halflings distancing themselves to insure their race as a whole would survive. So the Oana worked from the shadows to help their race. A few times a Oana cell has been exposed but most of these have been passed off as thieves guilds that use the name, so for now Oana is still a rumor and a secret.