Whetsheath (3.5e Equipment)
From D&D Wiki
Whetsheath: The Whetsheath was first used by a desert tribe, the Illandian people, who valued the edge of their blades greatly, since the metal strapped people relied on a type of light, short blade that weighed little, the Illandian Blade. The tribe eventually became slightly agrarian, settling occasionally on the edge of the great desert, but their reliance on sharp blades remained. Eventually, a trade caravan discovered the tribe, and carried back news of magically crafted daggers which could cleave a rock in two. Soon, the village was making a decent side business selling tribal 'magical' daggers with metal brought to them by traders. The secret, which only those trusted by the tribe know, is not the dagger, since the tribe would never sell their sacred blades to just anyone, and used ordinary blades from the caravan, but the sheath.
The whetsheath, which can be made of anything, but is often leather or wood by preference, is a custom fit sheath, and can be made for any weapon with an edge, blade, or point. The sheath is unbreakable, although dispel magic will cause it to revert back to an ordinary sheath. When the weapon is covered by the sheath, it magically sharpens the edge, making it sufficiently sharp to shave with instantly. It also keeps the blade in good repair, keeping it oiled or chalked, depending on the maker and the conditions.
If the blade is kept in the sheath for more than 7 days it becomes Keen, as by the spell. It will retain this ability for an hour out of the sheath, although an already keen weapon (as in under the affect of the sheath) that is placed into the sheath will have the duration of the spell increased to an hour.
 DM Notes
This item first appeared in a campaign in which the players were witness to a duel. The challenger was a barbarian, who thought that the scrawny desert nomad he had bumped into was too weak to have wandered so far north. The man, who eventually grew tired of the larger man's tirade, agreed to the duel, which ended when he cleaved the man's claymore in two.
That was when every person in the party wanted whatever that guy had.
Upon reflection, even our branch wielding druid wanted one.