ObjectivePGP is an open-source library for iOS and macOS
ObjectivePGP is an open-source library for OpenPGP encryption, decryption, signing, and verification in Objective-C and Swift. It enables developers to add PGP-based security to iOS and macOS apps.
iMailist is a software allowing the sending of mails to format HTML to a whole mailing-list.
The program is written in Objective-C/Cocoa and works on Mac OS 10.3
Keychain Framework is an Objective C Foundation-based framework for accessing Keychain and Security services under MacOS X. It provides convenience wrappers around the CDSA library included with MacOS X, facilities for manipulating keychains, and more.
Mailcash if a plugin for Apple's Mail program that provides hashcash support - that is, verification and generation of hashcash stamps. Refer to <http://www.hashcash.org/> for more information about Hashcash.