RetroShare is a Open Source cross-platform, private and secure decentralised communication platform.
It lets you to securely chat and share files with your friends and family, using a web-of-trust to authenticate peers and OpenSSL to encrypt all communication.
RetroShare provides filesharing, chat, messages, forums and channels
http://retroshare.sourceforge.net/

It started as a secure, single floppy, bootable Linux distribution for storing PGP keys and then encrypting, signing and wiping files. At some point it became an exercise in over-engineering.
http://tinfoilhat.shmoo.com/