7-Zip

7-Zip is a free file archiving tool that compresses data and stores them in a folder named "archive." However, it is still an excellent file encryption program for the computer. It's mostly compatible with Windows, Mac OS X, and Linux. It's worth mentioning that the official distribution of this file encryption program is only for Windows, but there are unofficial versions for Linux and OS X as well.

7-Zip can encrypt a single file or a whole drive using just the key you hold. This tool is absolutely free to use, even for business purposes, and it includes 256-bit AES encryption. The single file can be encrypted with a password and transformed to an executable file that will self-decrypt when it reaches the designated recipient, in addition to the security key.

Detailed information:
Price: Free
Platform: Linux, Windows
Website: https://www.7-zip.org/