Windows only : File encryption utility PixelCryptor doesn’t use a textual password to encrypt your files, it uses a digital image. Lock up your PixelCryptor file package like a drum and set an image as the key. The more complex the image, the more secure your encrypted folder. Then, on another PC with PixelCryptor installed (or available on a thumb drive), unlock the folder contents only with the image you used to encrypt it. PixelCryptor isn’t open source (so perhaps not as well-developed or supported), but it looks like a viable alternative to our beloved TrueCrypt.
PixelCryptor is freeware for Windows only.