(covers information from several alternate timelines)
A tricobalt device, also known as a tricobalt charge or tricobalt warhead, was a type of tricobalt explosive device utilized as a missile. (DS9: "Blaze of Glory") At extremely high yields, they were capable of producing disruptions or even ruptures in subspace. (VOY: "The Voyager Conspiracy").
In 2155, in the mirror universe, the Tholians detonated a tricobalt warhead inside the gravity well of a dead star and successfully created an interphasic rift to the parallel prime universe of 2268. (TOS: "The Tholian Web"; ENT: "In a Mirror, Darkly")
Tricobalt devices were not standard issue weapons on Starfleet starships, but were sometimes carried in addition to photon torpedoes. A pair of tricobalt devices, with a yield of 20,000 teracochranes, twice the necessary yield, were used by the USS Voyager in order to destroy the Caretaker's array in 2371. The explosion destroyed the station, leaving only particulate dust, vapors, and metallic fragments. The double yield, coupled with the unusual nature of Voyager carrying the weapons, led a malfunctioning Seven of Nine to reason in 2376, that Voyager expected to find the Caretaker's array and destroyed it to establish a Federation military presence in the Delta Quadrant. (VOY: "Caretaker", "The Voyager Conspiracy")
By 2373, the Maquis had been able to procure tricobalt explosives. In that year, Captain Benjamin Sisko theorized that they could be used in cloaked missiles that were supposedly on their way to Cardassia Prime. (DS9: "Blaze of Glory")
In Star Trek Online, tricobalt devices are a purchasable weapon for starships. They do the most kinetic damage of any torpedo in the game out-damaging quantum torpedoes several times (if used with the correct skills), but at the cost of a very long recharge and being destructible in flight.