A Starfleet system unveiled on Frontier Day in 2401 that lets every ship in a fleet be networked and manoeuvred as a single unit, and which the Borg turned against the Federation.
Fleet formation mode ties the helm, weapons and defences of many starships together so that they can move and fight in perfect coordination. Starfleet presented it as an answer to the threats of recent decades.
It is demonstrated in the Star Trek: Picard episode Vox, when Admiral Elizabeth Shelby aboard the USS Enterprise-F leads the assembled fleet over Earth for the Frontier Day celebrations. At that moment the Borg signal activates the younger officers who had been altered through the transporters, and the linked ships fall under the control of the Collective at a stroke.
In The Last Generation the captured fleet bombards Spacedock and Earth's defences until the rebuilt Enterprise-D destroys the Borg transmitter at Jupiter.