Dark Wallet: Next-gen privacy and security for Bitcoin, crowdsourced.

This is still in alpha and not stable, but is feature complete. Play with it on testnet (play money). What is revolutionary about it: 1) Trustless mixing is as easy as installing a browser extension. This combines users’ coins together before encoding them into the Bitcoin blockchain. 2) Stealth addresses allow the sender to generate new addresses for the receiver, and send funds without anyone watching the blockchain knowing the receiver is the owner of the original stealth address. 3) Multisig transactions - meaning you could set up a wallet that required 2 of 3 people (or devices!) to sign any transaction. This is sort of like multifactor auth. For one thing it would mean you could store your bitcoins at an online bank and not have to trust them. You give them one key, keep two for yourself, and require 2/3 keys to sign. No more risk of a Mt. Gox situation.