VeraCrypt is a high-security, cross-platform encryption app from Idrix EURL (Mounir Idrassi), based on TrueCrypt, which was discontinued last year. Features include on-the-fly volume encryption (like Apple's encrypted disk images or FileVault), hidden volumes, hardware-accelerated encryption (e.g. Intel AES-NI support), support for various algorithms, security token and smart card support, and the ability to load TrueCrypt volumes with "enhanced security" vs. TrueCrypt (particularly for brute-force attacks). VeraCrypt 1.13 is free, open-source software for Mac OS X 10.6 and up and requires OSXFUSE 2.3 or later.
It should also be noted that TrueCrypt has finally been audited and nothing untoward was discovered. Plenty of things to "do better" but no back doors.
What if one uses dual-boot (Win-Linux) and wishes to access the encrypted drive? It would be an entirely separate and external HD I am referring to. I have never tried either of these encryption methods.
Works fine @Brokor . Since it's your computer you can install VeraCrypt under both OS. If you want to exchange encrypted information with someone else, you can leave a small part of the disk unencrypted and put the portable version of VeraCrypt on it, so the other person doesn't have to install it Just make sure it's placed on the unencrypted part