Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
Easy Message - Easy Message app comes up with features to help users in effortlessly sending text messages to a phone number, which is not in the contact list.
OpenKeychain - OpenKeychain helps you communicate more privately and securely.
Seecrypt - Seecrypt app allows users to do secure voice and conference calls by using advanced encryption features so they can contact their friends, colleagues, and family members without any privacy issues.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Silent Phone - Silent Circle is a secure communications firm offering enterprise communications solutions including software, devices, and services.