In the Star Wars universe the Darksaber is a dark lightsaber built by a Mandalorean named Tarre Vizsla over 1,000 years before the Battle of Yavin. There is only one Darksaber in the universe and what makes this weapon so unique is that unlike the standard Kyber crystal that are used to construct a lightsaber the crystal in this weapon is a conduit for all Force energy that draws in all light and color leaving the blade black with a white aura around the blade. Additionally, unlike the standard lightsaber the Darksaber's blade is flat and curved to a point like a sword.
Darth Maul is one of only two people, outside of House Vizsla, to wield the blade and he is one of my favorite characters in the canon storyline.