The Premonition class was a class of Federation Starfleet starship built in an alternate timeline in which the Federation had been almost completely destroyed by a Borg invasion begun in 2376. The class was similar in size and configuration to the Sovereign-class, though was a distinctly different design - the most notable difference being a third, pink hued, nacelle supported by struts coming out of the top of the saucer section, presumably the vessels' temporal drive.
The Premonition-class was capable of time travel, using its temporal drive to open temporal gates, and could also generate gates for other vessels to travel through. In addition to phasers and photon torpedoes the class was also endowed with other temporal technologies, including the Gemini effect which could create a temporal duplicate of a targeted vessel, and the ability to generate a temporal stasis field which could freeze an area of space in time.
The only known vessel of this class was the USS Premonition, which under the command of Captain Thaddius Deming was sent back in time to try and prevent the Borg from destroying the Federation. The Premonition was pursued through time by two Borg spheres, but was rescued by the USS Enterprise-E and was able to deliver its warning of the impending invasion. Despite this the Borg still initially succeeded in assimilating Earth. However, thanks to the Premonition's presence the Enterprise was able to travel back in time to further intervene, and this time successfully stop the invasion. Before returning to her own time the Premonition made one more trip further back in time to prevent the Borg from destroying the USS Enterprise-D at an earlier date in an attempt to stop Jean-Luc Picard from ever interfering in their plans. (TNG video game: Armada)