Following are the listing of tools that can be used for various purposes in Linux, Windows environments and those which are available FREE of cost for downloads. This is the first compilation and will continue to grow as time progresses.
CryptoLab
CryptoLab is a cryptography application used in Windows. It uses text-based encryption or decryption.
CCrypt
CCrypt is a command line encryption tool to encrypt the files of your choice. This employs Rjindael AES cipher (Advanced Encryption Standard) and is available here.
GAIM – Online chat encryption program
It is an instant messager protocol which encrypts the communication that happens across MSN, Yahoo, AIM, ICQ chatting applications. You can download it from sourceforge.
Kerberos
Kerberos is a network authentication protocol and can be downloaded from this location.
MCrypt
mcrypt is another command line tool which allows you to encrypt files that you specify on the command line using one of the encryption algorithms: Blowfish, Twofish, DES, TripleDES, 3-Way, Safer, Loki97, Gost, RC2, Mars, Rjindael AES, Serpent, Cast, Arcfour and Wake. This works in *nix and windows and can be downloaded from here.
OpenSSL
OpenSSL is SSL and TLS protocol implementation in C language based on SSLeay. Versions are available for both windows and *nix environment and it supports many cryptographic algorithms like Blowfish, Camellia, DES, RC2, RC4, RC5, IDEA, AES.
You can read more about it from wikipedia.
Password Safe – For encrypting and storing ALL your passwords in one Safe. This can be downloaded from http://passwordsafe.sourceforge.net
PGP – Pretty Good Privacy also knows as GPG – Gnu Privacy Guard
Poor man’s entry into the world of encryption. Free version of the tool is available at http://www.gnupg.org. It is used to encrypt document or messages with public key encryption.