The Sin cloak is a disposable used by Noa Rylie in Metal Shadow Prelude. It is a length of black fabric once possessed by the Un-Sin. They gave it to Noa to help her flee danger. Who designed the cloak was never specified in the Prelude.
The cloak has magical properties. It has a mind of its own, and can shapeshift into anything (including a stallion, a bird, and a wolf). It cannot expand in size. It apparently weighs an extreme load. Despite this, it can also defy gravity.