Best open-source symmetric-only file encryption utility apart from PGP? [closed]

Best open-source symmetric-only file encryption utility apart from PGP? [closed]

I need to e-mail a file to someone with whom I have already negotiated a password. What are reputable, reliable and open-source tool with simple UI? An example for disk (as opposed to file) encryption is TrueCrypt. Platform is windows but available linux port is a plus.