The Caatati are a spacefaring humanoid species apparently native to the space near Borg territory in the Milky Way's Delta Quadrant. At some point in the 24th century, their civilization was nearly entirely assimilated by the Borg. Only 27 ships escaped carrying a few hundreds of individuals who were forced to wander the quadrant as nomads, pleading alien vessels for food and other provisions, especially thorium, an element essential for their technology and which they are no longer capable of replicating. Out of desperation, the Caatati have been known to threaten violence against weakened ships if they fail to comply to their needs, even if the ship in question has previously assisted them. Ironically, despite their (justified) fear and prejudice of the Borg, it was a former Borg drone named Seven of Nine who later offered them the technology to replicate thorium in exchange for the USS Voyager 's warp core which had been ejected from the ship and claimed by the Caatati as a way to bargain for further supplies.
Curiously, members of this species have been observed in the Deep Space 9 station at the other side of the galaxy. It is hence possible that the Caatati civilization extends or has previously extended into the Gamma Quadrant and has access to the wormhole leading to the station. Another possibility is that these represent outcasts who have explored the galaxy on their own. In any case, save for the possibility of these beings belonging to a different species which happens to look identical to the Caatati (the same way that many unrelated Star Trek species look externally identical to Humans) it is likely that the 27 nomad ships encountered by Voyager are not really the last ones of the species, even if they may believe themselves to be.