A cylinder of rough cast iron (invulnerable to harm from the mortal plane) with an oddly-shaped keyhole on each end. It comes without any accompanying key, though: the lock is sentient and capable of speaking and understanding any language. Above all else it desires to serve the ideals of freedom; specifically the greatest freedom for the most people. Of its own accord it can merge with other objects, lock them tight, unlock, and disengage. But to do any of these, it must be convinced that doing so will serve the cause of freedom.
The Lawless Lock is not very bright. It easily loses the thread of complex philosophical or ethical arguments and responds to confusion by promptly forgetting the entire offending conversation. It tends to believe what people tell it, taking their words at face value. On the other hand, it will forever remember someone who has demonstrably lied to it, and make a point of ignoring what they have to say thereafter.
It may seem paradoxical for a lock to value freedom, but as with most sentient beings it goes out of its way to downplay contradictions between its own beliefs and actions. Tyrants have been known to imprison political foes by convincing the lock that their captives threaten the greater freedom of the populace in some way.
(The name for this week’s magic item comes from The Forge.)