Specifically knives (not swords) - knives that do more than cut the usual intended materials. Bodkins, daggers and dirks okay, but keep 'em short. ;)

Examples: a knife that talks; a knife that cuts through reality; a dull knife that is only sharp against one item; a knife that glows periodically (like Sting, Bilbo's blade); enchanted or cursed knives; knives that bring to life what they've carved, etc.

See also:
Portal is an object (port key): https://www.goodreads.com/list/show/1...