APG es una implementación de OpenPGP para Android.
Licencia: GPLv3+
During the time APG developement was asleep, a fork of it called OpenKeychain was developed by Dominik Schürmann and quite a few contributors. This fork overhauled most of APG's GUI to work better with the current Android versions. It also introduced many awesome features.
APG 1.1.0 incorporates most of those changes and I'm very grateful for and impressed by their work.