GnuPG - GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP).
docNCRYPT - docNCRYPT is a cybersecurity platform which only focuses on its core services in protecting your email directly from the different email service provider and allows you to integrate your business email portal in the online service.
Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
encryptomatic - encryptomatic is a smart email encryption software which provides tons of tools in encryption protocols for secure communication and business transaction.
PGP Tool - PGPTool allows you to encrypt and decrypt files. It's free and easy to use.
Protected Trust - Protected Trust works to enable businesses to experience high productivity and security with Microsoft 365 and Surface.