The password strength meter uses some excellent logic to determine how likely a robot will be able to guess a password. Dan Wheeler of Dropbox, Inc. took on this project for hackweek at Dropbox. He "thought it’d be fun to build an open source estimator that catches common patterns, and as a corollary, doesn’t penalize sufficiently complex passphrases like correcthorsebatterystaple".
Use it yourself for your next project. Or check out the demo to learn more.