Simpleaf is a very simple and surprisingly efficient handwriting memo app.
Simpleaf is accessible from the notification area. It allows you to take a note from any app without going back to the home screen.
You can take a note, at the same time you are looking at the screen by making simpleaf translucent.
Written memo can be transmitted to mail apps or Evernote.
(Traffic can be saved by specifying an image size and format.)