Mac GNU Privacy Guard 2.0
Mac GNU Privacy Guard (Mac GPG for short) is, after a fashion, the Mac OS X port of GnuPG, licensed under the GNU GPL.
The aims of the project are to make GnuPG easy to install, develop a framework to make it easy for other developers to incorporate GnuPG functionality into their applications, write services to allow for the use of GnuPG functions in most Cocoa applications, and write a Mac GPG Keys type application so that you no longer have to go to the commandline to manage your keys. For those who don't know, GnuPG is a free OpenPGP client (PGP == Pretty Good Privacy). It can encrypt text (usually e-mail or other messages sent between people) and sign text to prove who wrote it.