#6754
DiskCryptor is a free and open-source full-disk encryption solution for Windows, developed by Xanasoft (DavidXanatos) from Austria, the creator of Sandboxie. It can encrypt entire hard drives, individual partitions, or external storage devices. It was originally developed as a free alternative to DriveCrypt Plus Pack (developed by SecurStar) and PGP WDE (Whole Disk Encryption, developed by Symantec). The latter two have long stopped development, while it is constantly being updated and maintained by a team of developers, ensuring that it stays secure against any potential vulnerabilities.

#5069
PGP (Pretty Good Privacy) is currently the best and most popular data (including texts, e-mails, files, directories, partitions, and whole disk) signing, encrypting, and decrypting program, developed by Phil Zimmermann in 1991. Its source code is open, and it has withstood the challenges from thousands of top hackers around the world. It turns out that PGP is still the most secure encryption software in the world for now (until the popularity of quantum computers, I think). Without a password, no one can decrypt the data encrypted with it!