Keybase is a new and free security app for mobile phones and computers. For the geeks among us: it's open source and powered by public-key cryptography.
[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.
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.
FileVault is a method of using encryption with volumes on Mac computers. Encryption and decryption are performed on the fly.
A secure virtual hard drive, powered by the cloud. CloudDrive allows you to store encrypted data in various cloud based service providers like Google Drive, Dropbox, Onedrive, etc.
The realcrypt application in the RPM Fusion repo is an encryption application based on truecrypt, freely available at...
ProxyCrypt is a command line tool that creates encrypted volumes within a file or a hard drive.