GPG4Win is not available for Mac but there are some alternatives that runs on macOS with similar functionality. The best Mac alternative is GnuPG, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to GPG4Win and eight of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to GPG4Win are GPGTools (Freemium, Open Source), GPG Suite (Paid, Open Source), PGP Tool (Free, Open Source) and OneTime (Free, Open Source).
GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.
Almost everyone thinks GnuPG is a great alternative to GPG4Win.
OneTime is an open source encryption program that uses the one-time pad algorithm to allow two parties to communicate privately. It has features to assist with the bureaucracy of pad management, and comes with built-in help. OneTime requires Python 2.