ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
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.
Tutanota - Get your encrypted mailbox for free.
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.
Mailvelope - Mailvelope open source project. OpenPGP in your browser.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.