Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
WAMR - WAMR – Recover Deleted Messages and Status Download is a powerful app that helps you recover text messages and media attachments.
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.
SMS Plus - SMS Plus app offers features that let you forward text messages through internet connection as well as through other social media platforms.
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