The Borg Cooperative were originally a group of escaped Borg.
At some point in 2368, a Borg cube traveling through the Nekrit Expanse was disabled, apparently by an electrokinetic storm. This resulted in the death of the majority of the Borg on board and separated the survivors from the Collective. Because the equipment on the cube was no longer functioning, their collective consciousness collapsed and they regained their former senses of identity and individuality.
The 80,000 former Borg transported to the surface of a nearby Class M planet, and, free and grateful for the opportunity to re-experience their own thoughts and memories, began re-building their lives as individuals.
Many races were represented on the new planet including a number from the Alpha Quadrant who were assimilated during the Borg incursion in 2366. They included dozens of different races including Humans, Romulans, Cardassians, Klingons, Farn and Parein.
Borg no more
Many of the former Borg found ways to remove most of their cybernetic Borg appendages and slowly became something akin to their old physical selves. Their natural skin pigmentation returned, and their memories re-emerged. However, many of the former Borg belonged to races which had historically been enemies. Without the unifying force of the Borg collective consciousness, they struggled to coexist, and as their personalities returned, so did their original hatreds and differences.
In the midst of this chaos, a group consisting of a few hundred survivors, including Riley Frazier and Orum, set up a cooperative in an attempt to find a peaceful solution to the conflicts. Built on tolerance, shared responsibility and mutual respect, the cooperative worked together to create a new life and they began to grow all their own food in a communal garden. However, desperately short of supplies, the other former Borg were determined to overpower them, and the cooperative was forced to defend itself.
The former Borg were unable to remove all of their Borg components, and they were still equipped with neural processors, which were implanted in their nervous systems. The cooperative was able to temporarily re-initiate the connection between their minds using a portable transponder, to create a mini-collective within a small group.
This link enabled them to communicate with each other telepathically and to send healing neuroelectric energy to one another's organic or inorganic body parts. It seemed the members of the cooperative were able to take advantage of their Borg abilities while still maintaining their distinct personalities. They shared one another's thoughts; the connection they had to one another far exceeded the intimacy generally experienced by Humans, and could be quite erotic. Each new mind that was added to the group, even temporarily, extended the interior world of the cooperative as each individual brought new energy, hope, ideas, knowledge, and memories.
Horrified by the chaos around them, the cooperative planned to force the disparate races on the planet to live in harmony by re-establishing the neural link between all of the former Borg on the planet, recreating the collective. The cooperative believed this new collective would not be dominated by the Borg desire to assimilate other races and that it would be able to cooperate and solve problems to build a new society.
In order to reestablish the collective, the group planned to reactivate the neuroelectric generator on the abandoned cube and redirect it toward the planet. Within a few minutes this would generate a strong enough neuroelectric field to link all of the former Borg into a new collective.
However, the members of the cooperative had no means of returning to their starship. When Commander Chakotay of the USS Voyager crash-landed on their planet, they were finally given the opportunity they needed.
On returning to Voyager, he explained their plan to use the abandoned Borg cube to bring all the planet's inhabitants into a new collective mind and so stop the war. Although applauding the ideals behind the idea, Captain Janeway refused to allow the plan to proceed.
Using their communications array, the cooperative took over Chakotay's mind using a residual link between him and the members of the cooperative. They forced him to go to the Borg cube, where he restored power to the neuroelectric generator.
A new collective
With the generator active again, all of the former Borg were joined in a new collective. The cube and its remaining Borg inhabitants also reactivated; however the Cooperative activated the cube's self-destruct mechanism and destroyed it before it could take action against Voyager.
The new collective seemed benevolent and did not appear to be governed by typical Borg philosophy. It was clearly not connected to the rest of the Borg Collective, but there was no telling how much of a danger it could present in future. (VOY: "Unity")
In The Eternal Tide, Voyager returns to check on the Borg Cooperative after the Borg Collective is absorbed into the Caeliar- the race that unintentionally created them- after the Star Trek: Destiny series. Captain Chakotay learns from Riley that most of the Cooperative- having achieved a balance between working as a hive mind while exploring their individual desires and pursuits before the Borg were absorbed- has been reduced to a mere forty-eight, these few being the only ones left after their world was claimed by the Tarkons and the rest of them were absorbed into the Caeliar gestalt, these few having remained because they had become parents and did not want to abandon their non-Borg children. With Voyager's help, Riley and the others are able to relocate to the original abandoned Borg 'homeworld', where they can set up a new life as the world's atmosphere begins to regenerate in the absence of the Borg.