Encrypto

Encrypto is a program that allows you to encrypt individual files, for example so that you can email them as attachments without the risk that someone can intercept them and read them. It uses the AES-256 algorithm for encryption. You select a password and communicate this to the recipient through other means. They then use Encrypto to decrypt the file and read the contents.

All this is excellent except that:

• Encrypto is proprietary, not open source. This means it is not possible to see their code and assess if the cryptography is correctly implemented and if there are any backdoors or not.
• Encrypto creates the encrypted version of the file as a .crypto file. This seems exclusive to them, so it's not clear that any other app could be used to open the file, even if it also uses the AES-256 standard. Therefore, it seems like if you encrypt your files using Encrypto, you're locking yourself to Encrypto.
• 7-Zip is an open source alternative that does exactly the same thing, and therefore is not locking you in and you can check the code. However, 7Zip does not work natively on Mac.