[TrueCrypt is not exactly "Open Source", but the source is available. See the reviews to get more information.]Discontinued
The development of TrueCrypt was ended in 5/2014 after Microsoft terminated support of Windows XP. Windows 8/7/Vista and later offer integrated support for encrypted disks and virtual disk images. Such integrated support is also available on other platforms. You should migrate any data encrypted by TrueCrypt to encrypted disks or virtual disk images supported on your platform.
BitLocker Drive Encryption is a data protection feature that integrates with the operating system and addresses the threats of data theft or exposure from lost, stolen, or inappropriately decommissioned computers.
With EDS (Encrypted Data Store) you can store your files in the encrypted container to prevent unauthorized access to sensitive information.
Safeguard Your Personal Files SanDisk SecureAccess software creates a password-protected private folder on your SanDisk USB flash drive where you can store your most sensitive personal files. Your data will be protected with strong 128-bit AES encryption.
Protects Personal Data.Discontinued
The program is no longer updated. Last version, 3.0, released in August 2015, can be still downloaded from the official website.
FreeOTFE is a free, open source, "on-the-fly" (OTFE) disk encryption program for PCs running MS Windows and Windows Mobile PDAs (FreeOTFE4PDA).Discontinued
Discontinued per Wikipedia page (https://en.wikipedia.org/wiki/FreeOTFE)
Data encryption software by CryptoForge allows you to secure your sensitive data everywhere it goes with strong AES encryption. It features a file encryption module which allows you to encrypt files and folders of any type and size, on any kind of media, including external USB...
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