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.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Cellcrypt - Cellcrypt app provides features so you can enjoy secure conference calling, messaging, and sharing of documents.
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.