5 Free 256-bit Encrypted Voice Calls Apps With End-to-End Encryption

Secure email: ProtonMail is free encrypted email.

Secure email: Tutanota makes encrypted emails easy. #FOSS

An Inside Look at ProtonMail: End-to-End Encrypted Email - CryptoCoinsNews

Threema - Seriously secure messaging -

Tutanota: the Open-Source Encrypted E-mail Answer to Protonmail | Hacked