Silver Sword of Gith

The Silver Sword of Gith is an artifact sacred to the Githyanki. It was the first and most powerful of the silver swords and belonged to the Githyanki hero Gith. When Gith left her people to seek an alliance with Tiamat and she never returned, the sword was lost.

Neverwinter Nights 2
The Neverwinter Nights 2 games expanded on the sword's history considerably. It established that the sword was forged for Gith by Zerthimon. Ammon Jerro found the artifact but when he attacked the King of Shadows with it, it shattered into several shards, one of which buried itself inside the body of a baby who would grow up to be the Kalach-Cha. The Kalach-Cha collected the scattered shards, whilst being pursued by the zealous Githyanki and eventually reassembled them at the site where the blade originally shattered.

The sword had gained a couple of new powers due to the fractured nature of the blade, but since the final shard was still buried in the Kalach-Cha, it could not be restored fully. The blade was then used to defeat the King of Shadows.

Neverwinter Nights 2: Mask of the Betrayer
The history of the Sword of Gith is expanded further in this game. It turns out that the sword is the key to the Betrayer's Gate, a portal in a temple to Myrkul on the Plane of Shadow in Mulsantir that leads to the Fugue Plane. This Gate was used by Akachi the Betrayer, a priest of Myrkul that used the blade to try and take down the Wall of the Faithless.

Forgotten Realms: Demon Stone
The sword is central to the role of this game as well, though you do not find out why until the end of the game. The Slaad lord Ygorl desired the artifact to increase his own power. The sword is in the hands of Cireka, a Githyanki general and the two battled over it, pitting their armies against each other until their fight spilled over into Toril and Khelben Arunsun trapped them in a magical stone. When adventurers release the two, their fight resumes until Cireka is slain by the red dragon Caminus. Rannek of Nesmé retrieves the blade and uses it to help defeat Ygorl, he is concerned however, that the Githyanki will return to retrieve it at some point.