Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
YAATA - YAATA app offers features that let you send multimedia files such as images, videos, audio, and GIFs, etc.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS