Tiger Envelopes is a little program that lets you read and write email privately.

Envelopes is a personal mail proxy
that automatically encrypts and decrypts.
It uses standard OpenPGP encryption programs such as
GPG, Bouncy Castle, and PGP.
The Open Crypto Engine,
also developed by Tiger Privacy, is an API that talks to these
different packages.
It's all open source so anyone can verify that there's no spyware,
no malware, and no central control.

If you're really short on time and just want the buzzwords,
Tiger Envelopes gives you opportunistic,
layered encryption with p2p public key distribution.

Opportunistic
  
When two people use Envelopes, the encryption just happens.
All you have to do is keep using your email as usual.
Your mail is safe beginning with the first reply.

The first unprotected message is the last.

In case you encounter one of those rare and brave people who use
traditional email encryption, Envelopes also works with older OpenPGP mail
encryption packages that don't support opportunistic encryption.

Layered
  
Envelopes includes the Bouncy Castle encryption package so there's nothing
else you have to install.
But if you already have GPG or PGP,
Envelopes will encrypt your messages in layers.
Each protective layer is provided by a different encryption program.
To crack your message, an attacker has to crack all the layers.
A vulnerability in one encryption program doesn't compromise the message.
If any of them works, your message is safe.

P2P
  
Tiger uses a peer to peer key distribution protocol with no centralized
server.
That means there's no complicated Public Key Infrastructure to set up and
maintain, and no central tracking or control.
Envelopes creates keys for you and distributes public keys transparently.
You get a short note telling you when a new key arrives and
how to verify it.

Core
  
Tiger Envelopes starts with one-click cross platform installers and
automatic mail client configuration.
It quietly adds opportunistic, layered encryption with p2p public key
exchange.
The control panel makes complex key management and automated testing
simple.
The technology is all for just one purpose:
making your private email easy.