gpg4usb is described as 'easy to use, small portable editor with the possibilityto encrypt and decrypt any text-message or -file you want. For encryption it acts asa'. There are four alternatives to gpg4usb for a variety of platforms, including Windows, Apple Mail, GnuPG, GPG Suite and iPad. The best alternative is GPG4Win, which is both free and Open Source. Other great apps like gpg4usb are GPGTools (Freemium, Open Source), GNUPGK (Free, Open Source) and Pignus Encryption (Paid).