Tkpgp:

Encrypt, Decrypt, Verify, Sign, E-mail messages with a GUI interface to the PGP (Pretty Good Privacy) program pgp and/or the GPG (Gnu Privacy Guard) program gpg.

Keep an eye on the clipboard selection, Tkpgp's default is to place things you frequently want to cut and paste in the selection automatically. This provides a simple way to integrate pgp/gpg with other apps.

README
Download Unix (supports pgp 2.6.2 / gpg 1.4.0 or later) Version 1.0 released January 2010.
Download Windows (supports pgp 2.6.2 only) No longer maintained.