Knox!

[TrueCrypt is not exactly "Open Source", but the source is available. See the reviews to get more information.]

LUKS is the standard for Linux hard disk encryption. By providing a standard on-disk-format, it does not only facilitate compatibility among distributions, but also provides secure management of multiple user passwords. In contrast to existing solution, LUKS stores all setup necessary setup information in the partition header, enabling the user to transport or migrate his data seamlessly.

No encryption of dynamic disks, but command-line-encryption! Dynamic disks must be converted to basic disks with EasyUS Partition Master or Partition Guru before encrypting with Bitlocker. Windows BitLocker & "Bitlocker To Go" Drive Encryption is a data protection feature in Windows 10 Professional, Windows Vista Enterprise and Windows Vista Ultimate for client computers and in Windows Server 2008. BitLocker protects against data theft or exposure on computers that are lost or stolen, and offers more secure data deletion when computers are decommissioned. Bitlocker To Go (BTG) is essentially Bitlocker for external drives. It’s full volume encryption for all your USB drives: http://blogs.msdn.com/b/rockyh/archive/2009/03/01/bitlocker-to-go.aspx »

LibreCrypt (formerly DoxBox) is an open-source disk encryption for Windows and the successor of FreeOTFE

Cryptonite brings EncFS and TrueCrypt to Android. You can browse, export and open EncFS-encrypted directories and files on your Dropbox and on your phone. On rooted phones that support FUSE (e.g. CyanogenMod) you can also mount EncFS and TrueCrypt volumes. TrueCrypt is only available as a command-line version at this time.

The Gnome Encfs Manager is an easy to use manager and mounter for encfs stashes. It allows you to create encrypted directories, any file that is placed in such a directory will be encrypted.

DiskCryptor is the only truly free solution, provided under GNU General Public License (GPLv3), which offers encryption of all disk partitions, including the system partition. The main criteria for open-source software is the availability of its source code under one of the open source licenses. The only open-source alternative to DiskCryptor that has comparable features is TrueCrypt. However, because of the restrictive license under which TrueCrypt is provided — the TrueCrypt Collective License — TrueCrypt cannot be classified as a truly free software, as it places limits on the use and modification of its source code by developers. There are other alternatives with similar functionality, but they are fully proprietary ones, which makes them unacceptable to use for protection of confidential data. »

Cryptkeeper is a Linux system tray applet that manages EncFS encrypted folders.

Seahorse is a front end for GnuPG - the GNU Privacy Guard program - that integrates to the GNOME desktop. It is a tool for secure communications and data storage. Data encryption and digital signature creation can easily be performed through a GUI and Key Management operations can easily be carried out through an intuitive interface.

If your computer were ever to be stolen, are you certain that your personal information cannot be discovered? Jetico’s BestCrypt software automatically encrypts your files so that nobody can read the data unless they have the right password or keys.

FreeOTFE is a free, open source, "on-the-fly" (OTFE) disk encryption program for PCs running MS Windows and Windows Mobile PDAs (FreeOTFE4PDA).

The enterprise cryptographic filesystem for Linux

DCrypt is an encryption and decryption tool that combines in a smart way multiple algorithms. The combination of multiple strong algorithms makes it much more difficult for hackers to get the plain content of the encrypted file without the password.