AxCrypt is a freeware program that lets you easily encrypt any file or folder on your computer. You can choose a password or use a passkey file. It also has a really easy-to-use user interface –
right-click the file or folder you want to encrypt, hover over the ‘AxCrypt’ option, then choose ‘Encrypt’.
Only for Windows
Get it here: http://www.axantum.com/axcrypt/