Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
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.
OpenKeychain - OpenKeychain helps you communicate more privately and securely.
Message Peeping Tom - Message Peeping Tom is an app by HSTAR, offers features that let you read your messages without giving the read report to the sender.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
PhoneLeash: SMS/MMS forwarding - PhoneLeash: SMS/MMS forwarding app offers features that let you forward your desired text messages and multimedia messages to your email or your other mobile phone so that you can access them later.