2 factor authenutication (password) key files
the ability to use any files as a password (key files)
similiar to what truecrypt uses.
With EncFS it is possible to do this like so:
dd if=/dev/urandom of=/path/to/keyfile bs=1k count=2
encfs --extpass="cat /path/to/keyfile" /encrypted /decrypted
this refers to using a password and a keyfile together.