Non-Free implementations that aim for OpenPGP compliance. 

= ObjectivePGP
https://objectivepgp.com/

//iOS/macOS OpenPGP library

| Programming Language/Environment | Objective C |

= iPGMail
https://ipgmail.com/

//iOS OpenPGP application

= CanaryMail
https://canarymail.io/

//iOS OpenPGP application

| Programming Language/Environment | BouncyCastle |

= R2Mail2
https://r2mail2.com/

//Android OpenPGP application

= MailDroid
http://flipdogsolutions.com/

//Android OpenPGP application