Superweapon

"Long ago in forgotten times, when the Sith and Jedi fought for control of the galaxy, weapons there were, of unimaginable power."

- Yoda

Superweapon (also spelled super-weapon) and megaweapon were terms used to describe a weapon of extremely devastating power, possibly enough to destroy a planet.

History
Superweapons were used in ancient wars between the Jedi and the Sith. These weapons were powered by Kyber crystals. One such weapon existed on the Sith planet Malachor, the site of an ancient battle. The Sith Lord Momin constructed a weapon with the ability to destroy an entire city. He used this weapon to destroy a city before he and his acolytes were defeated by the Jedi.

Clone Wars
The Subjugator-class heavy cruiser Malevolence used by the Confederacy of Independent Systems during the Clone Wars was considered to be a superweapon, as was the electro-proton bomb developed by Sionver Boll.

Age of the Empire
The first and second Death Star built by the Galactic Empire were superweapons, employing a powerful superlaser weapon that was powered by massive kyber crystals. Admiral Conan Antonio Motti loved technology that created devastating superweapons. The Arc Pulse Generator, invented by former Imperial Sabine Wren was also classified as a superweapon. The Empire was believed to have created many types of superweapons. The Onager-class Star Destroyer, was a type of capital ship that utilized a kyber crystal superweapon. The Mass Shadow Generator, which was rumored to exist in realspace and hyperspace, was a rumored Imperial superweapon project. The Torpedo Sphere was a siege platform and space station. The Omega Frost was a rumored interstellar freeze ray and the Electro-Proton Bomb/Defoliator was based off the Electro-proton bomb and Defoliator from the Clone Wars.

Rise of the First Order
Approximately thirty years after the destruction of the second Death Star, the primary base of the First Order—Starkiller Base—harbored a superweapon built into the planet's crust that was capable of destroying entire star systems, as demonstrated during the Hosnian Cataclysm. The weapon was powered by drawing on the energy of a star, which eventually led to the planet's collapse during an attack by the Resistance on Starkiller's thermal oscillator.

Behind the scenes
Earlier versions of the 2015 film Star Wars: Episode VII The Force Awakens had the Resistance developing a superweapon known as the War-Hammer. In those versions, the War-Hammer would've been several times the size of a Star Destroyer and had the form of a massive ship with a huge front that could penetrate any shield and was able to deploy ships through it.

Non-canon appearances

 * Rogue One: Recon A Star Wars 360 Experience
 * LEGO Star Wars: Droid Tales Episodes I-III