From UFStarfleet Wiki
The following is derived from the Mission Logs of the USS Caracas and the minds her crew.
Borg Tribe Information
Following the death of the Borg Queen and infection of the Borg Collective by a Virus (a joint effort by Admiral and Captain Janeway), the Borg Collective fractured, with the stronger minded Drones taking over other Drones and Ships within their range, forming a type of "Tribe".
These 'tribes' have varying amounts of drones and ships, as well as various amounts of power. Depending on their leader, a tribe may have as little as 1 ship and a few hundred drones, to a small fleet with thousands of drones.
The goals of these tribes are also different. The aim of achieving perfection is no longer the driving goal of the Borg. Depending on the personality of each tribe's leader, their goals differ. Goals could be anything, from the original goal of achieving Perfection, or re-uniting the entire collective, to achieving peace, or simply surviving.
The tribes are in varying amounts of disarray. Some of them are unable to perform the repairs their ship(s) need, and so make easy targets for other tribes and other species. Some have been infected with the original virus, and cannot perform all their functions correctly. Others, work exactly as they did when they were part of the collective, and are a serious threat to anyone who goes up against them.
Suffice to say, no matter which tribe you go up against, they are still dangerous. Avoiding a confrontation should be a high priority unless you have a fleet of ships nearby. In the event that you don't, and can't avoid a confrontation, you should hope that you come across one of the weaker tribes with older ships, or your fate will be sealed.
Known Borg Tribes
It is unknown exactly how many tribes there are, or for the ones that are known, how strong they are. The United Federation Starfleet, and the USS Caracas in particular, have only encountered a few tribes.
One of which attempted to assimilate an entire planet, and was ultimately destroyed by the USS Caracas, USS Orion, USS Colossus and USS Athena. The Orion was destroyed in this battle, and the Caracas was critically damaged, requiring her crew to abandon ship. The fleet however, was able to destroy the 2 cubes (1 destroyed by the Caracas earlier - an older cube), and 3 smaller ships. All the ships were in disrepair, the tribe apparently unable to keep them sufficiently repaired.