
For those of you who are interested, here's a list of well-known free and open source encryption software for Linux:
TrueCrypt
TrueCrypt is one of the most popular disk encryption tools around. It can encrypt and decrypt files on-the-fly (real-time) as needed without user intervention beyond entering the passphrase. TrueCrypt is capable of creating a virtual encrypted disk within a file or a device-hosted encrypted volume on either an individual partition or an entire storage device. It currently uses the XTS mode of operation but is backward compatible with older volumes.
Here are some of the main features of TrueCrypt:
* Creates a virtual encrypted disk within a file and mounts it as a real disk.
* Encrypts an entire partition or storage device such as USB flash drive or hard drive.
* Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.
* Provides plausible deniability, in case an adversary forces you to reveal the password.
* Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.
GNU Privacy Guard (GnuPG or PGP)

Some of its features include:
* Full OpenPGP implementation
* Full replacement of PGP
* Easy implementation of new algorithms using extension modules
* Does not use any patented algorithms
* Can be used as a filter program
* Better functionality than PGP and some security enhancements over PGP 2
* Decrypts and verifies PGP 5, 6 and 7 messages
* Supports ElGamal, DSA, RSA, AES, 3DES, Blowfish, Twofish, CAST5, MD5, SHA-1, RIPE-MD-160 and TIGER
* Integrated support for HKP keyservers
More about GnuPG HERE
OpenSSL

More about OpenSSL HERE
Seahorse
Seahorse is a simple and easy-to-use GNOME front-end application for managing encryption keys such as PGP and SSH. It also integrates with nautilus, gedit and other places for encryption operations. The program supports HKP and LDAP key server.
The following are some of its features:
* Encrypting/decrypting/signing files and text
* Managing your keys and keyring
* Synchronizing your keys and your keyring with key servers
* Signing keys and publishing
* Caching your passphrase
* Backing up your keys and keyring
Seahorse is a simple and easy-to-use GNOME front-end application for managing encryption keys such as PGP and SSH. It also integrates with nautilus, gedit and other places for encryption operations. The program supports HKP and LDAP key server.
The following are some of its features:
* Encrypting/decrypting/signing files and text
* Managing your keys and keyring
* Synchronizing your keys and your keyring with key servers
* Signing keys and publishing
* Caching your passphrase
* Backing up your keys and keyring
mcrypt

More about mcrypt HERE
If you know of other free and open source encryption software that you would like to add to our list above, please share them with us via comment.