The Ebony Blade is a katana (one-handed blade) with two enchantments, and the Daedric Artifact of Mephala. The sword is attained by completing a quest for Mephala.
While not quite as powerful as Boethiah's Goldbrand, the blade does have the Silence and Absorb Health Enchantments, which are helpful against mage enemies. It absorbs eight points of health on hit, and the victim will not treat it as an armed assault. It is useful whilst doing some of the more stealthy Dark Brotherhood quests.