In Starfleet Battles and Starfleet Command, the Hellbore Cannon, most frequently called just 'Hellbore', is the preferred long-range heavy weapon of the Hydran Royal Navy.
Hellbores are capable of dealing significant damage at long range, and are second only to plasma torpedoes in close-in striking power. A single hellbore uses 2.5 units of energy per turn and takes 2 turns to charge in standard mode. The damage inflicted is enveloping, that is, it strikes all shields on the target. 50% of the damage is inflicted on the weakest shield, the balance is divided across the other five. This happens regardless of which shield it strikes. Even if the hellbore bolt strikes a downed shield, it still deals enveloping damage. The exception is if all shields are at equal strength, then the damage is divided by six and applied to all shields.
If facing a hellbore-armed opponent, do not allow them to drop any of your shields. If they do, and you take a hellbore hit, you will sustain internal damage regardless of what facing was struck. If you are playing as the Hydrans, or as a hellbore-armed Orion Pirate, take advantage of this fact to score internals on opponents as they turn their downed shields away from you.
Hellbores are exclusively an SFB and SFC weapon. They have never appeared (or at least, were never named) on Star Trek.