eCryptfs!

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

AES Crypt is an advanced file encryption utility that integrates with the Windows shell or runs from the Linux command prompt to provide a simple, yet powerful, tool for encrypting files using the Advanced Encryption Standard (AES). A Java library is also available for developers using Java to read and write AES formatted files.

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 »

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.

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.

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. »

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

LUKSUS is a tool that creates an encrypted volume and filesystem on a hardrive or other storage media as well as a filecontainer.It can use the following encryption facilities: LUKS, Truecrypt and GELI.

The realcrypt application in the RPM Fusion repo is an encryption application based on truecrypt, freely available at http://www.truecrypt.org/ . It differs from truecrypt in only the following ways:

TruPax generates TrueCrypt - compatible container files from arbitrary sets of files and folders. Such files match exactly the size of the contained material and can be mounted by TrueCrypt, but also directly extracted using TruPax itself. Latter also works for containers formatted with FAT32 by TrueCrypt itself, thanks to fat32-lib. For all of that there are no administrator rights required when using TruPax.

LUKS Manager provides on-the-fly encryption (AES by default) to virtual folders on Android devices.

ProxyCrypt is a command line tool that creates encrypted volumes within a file or a hard drive.It works as a "proxy" for the ImDisk Virtual Disk Driver .