Downloading GPGMail 2.1 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. GPGMail for Mac can also be called "GPGMail Uninstall". The application lies within Communication Tools, more precisely E-mail.
The most popular version of the tool is 2.0. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The actual developer of this free software for Mac is GPGTools Project Team.
From the developer:
GPGMail is an open source plugin for Apple Mail. It brings the functionality to sign, verify, encrypt and decrypt mails using the OpenPGP standard.
Please have a look at the getting started and FAQ section. It would be nice to tell Apple to support bundles for Mail.app officially.
You may want to check out more Mac applications, such as Enough, gFeeder or Seesmic for Facebook, which might be related to GPGMail.