Excalibur

 was the strongest sword in the game prior to PC v1.2, but has now been superseded by the True Excalibur and True Night's Edge. It is part of the Hallowed weaponry set. Excalibur can continuously attack, which can be useful for charging into a group of enemies. Like all Hallowed weapons, Excalibur gives off a faint glow and emits a sparkle effect when swung.

Trivia

 * The sword's name comes from Arthurian legend, where Excalibur is the sword of King Arthur which is either pulled from an anvil on a stone or given to him by the Lady of the Lake. Depending on the telling of the legend, Excalibur is a magical weapon and/or a symbol of the rightful ruler of Britannia.
 * Excalibur is said to be the holy sword of the gods. This is reinforced by the fact that the sword in-game is a Hallowed weapon.