Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
Encrypto - Encrypto lets you encrypt files before sending them to friends or coworkers.
OpenKeychain - OpenKeychain helps you communicate more privately and securely.
File Lock PEA - Password-encryption of files and directories. File PEA encrypts files and folders with authenticated encryption to protect confidentiality and integrity. The program uses memory-hard key derivation functions to prevent custom hardware attacks.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Unicode Crypter - Encrypt and Decrypt Unicode!