VeraCrypt

https://en.wikipedia.org/wiki/VeraCrypt

VeraCrypt is a source-available freeware utility used for on-the-fly encryption (OTFE). It can create a

virtual encrypted disk within a file or encrypt a partition or (in Windows) the entire storage device

with pre-boot authentication.

Incorrect answers:

PGP - designed by Phil Zimmerman as a freeware e-mail security program and was released in 1991.

It was the first widespread public key encryption program.

VPN - A virtual private network (VPN) extends a private network across a public network and enables

users to send and receive data across shared or public networks as if their computing devices were

directly connected to the private network. Applications running across a VPN may therefore benefit

from the functionality, security, and management of the private network. Encryption is a common,

although not an inherent, part of a VPN connection

Cryptool - an open-source project that focuses on the free e-learning software CrypTool illustrating

cryptographic and cryptanalytic concepts. According to "Hakin9", CrypTool is worldwide the most

widespread e-learning software in the field of cryptology.