The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.
Scanbot - Scanbot is a mobile app that allows you to use your device's camera as a document scanner. The app is capable of scanning a large number of source materials, and it can handle QR codes as well.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Scanner Pro - Scanner Pro turns your iPhone into portable scanner in your pocket.
Geary - Geary is an email application built for GNOME 3.
Genius Scan - On The Go.