PassPack currently in Beta release, is free, secure online Password Manager, that lets you store millions of passwords to use anytime, anywhere. PassPack uses a double access technique, and is based on the Host-Proof Hosting Ajax Pattern. The "Pack" in PassPack comes from that bundle of locked up passwords inside your Account. You can read more about this on the PassPack Blog.
PassPack has taken various measures to ensure the integrity and secrecy of the Passwords. The Security Overview covers them in detail.
“With AES encryption (the same as used by the US Government) and an SSL Secure Connection, your data travels safely over the internet. But let's suppose a hypothetical "bad-guy" gets into our servers, all he'd find would be a bunch of illegible data. If he's determined to crack this data, he'd have to guess the Pass and Packing Key in order to reverse the packing process - to date, this type of brute force attack on AES is considered impossible. That makes PassPack an unattractive target.”