Owners of some of the previous gen Galaxy Note devices who have been a bit jealous of the cool new "Screen-Off Memo" feature in the Galaxy Note 5 might see this as welcome news. Third party devs have ported the feature to the Galaxy Note 3, the Note 4 and the Note Edge.
If you are unfamiliar with this feature, it's you basically can take the S-Pen while the device is off, but can start writing on the display as if you’re just writing on a small notebook. Very slick!
Here's a link with full instructions and downloads: [APP] Screen Off Memo [Update: 21 Sept 2015]