Whether it's thanks to Star Wars: The Clone Wars, Star Wars Rebels or most recently in The Mandalorian, the Darksaber has become an iconic weapon in the hands of heroes and villains alike. However, while the existence of the Darksaber is a recent addition to the Star Wars canon, there's a version in Legends that is remarkably different.
In the mid-90s, Kevin J. Anderson expanded the Star Wars Legends universe with his numerous novels. His book titled Darksaber refers to the superweapon that exists within the novel.
Darksaber takes place twelve years after the events of A New Hope. Luke and Han are on Tatooine, searching for a way to contact Obi-Wan Kenobi from beyond the grave in order to help Luke's girlfriend, Callista, reconnect to the Force. However, along the way, he learns not only that the remnants of the Empire are coming back to cause problems, but that a Hutt crime lord named Durga has recruited the Death Star's designers to create his own superweapon: the Darksaber. Essentially, Durga decides to incorporate the Death Star design into a mobile ship that can travel across the stars. The weapon is basically a giant ship shaped like a lightsaber, hence the name.
The Darksaber is equipped with a super laser, powerful enough to obliterate planets. On paper, this sounds much like the Star Destroyers Palpatine created for the Final Order in The Rise of Skywalker, only larger. However, during the events of the novel, it is not fully operational, just being a massive ship.
Obviously, the Darksaber in the novel is distinctly different from the Darksaber in the current Star Wars canon, which is essentially a modified lightsaber. The non canon Darksaber, despite being shaped like the hilt of a lightsaber, is a planet destroyer. The "lightsaber beam" the weapon generates is not a slashing weapon, but essentially a laser blast designed to obliterate worlds.
Durga ends up residing in the Hoth system where he kills a Rebel operative who finds him. This sends a signal to Luke and the gang, which results in the Rebels finding and pursuing the still in-construction Darksaber. The weapon fails to actually fire when Durga tries using it. During the chase, the Darksaber is struck by two asteroids, with its absurd design being the key reason it can't navigate an asteroid belt. It's destroyed without being blown up by the Rebels, and they win with very little difficulty. The Darksaber might have been powerful, but it was destroyed with even less effort than the Death Star.
Ultimately, the old Darksaber is just a clunky, easily-destroyed spaceship that had the potential to be just as deadly as the Death Star. In regards to fan media, while the old Darksaber was more powerful, it lacked the practicality, applicability or legacy of the modern Darksaber. There was no passing of the sword across generations, no ancient techniques that designed it -- it was just a knock off Death Star.