Paper by 53 has received an update in preparation for the relase of Pencil, a stylus designed by the company for use with Paper. This enables the palm rejection, eraser, and blend capabilities of Pencil. Pencil's features will only work with Paper, though you can still use Pencil as a regular capacitive stylus in other apps. Paper's expressive ink engine has also been rebuilt to feel faster and more responsive with all of the app's tools.
You can download this update from the App Store now, and Pencil is due to ship soon.