Path is a private social networking application that allows you to create a path (comments, photos, location, etc.) and share it with a select number of people. Their most recent update is absolutely stunning. Arguably the best looking application on the iPhone at the moment.
Here is a good look at their application from Geoff Teehan. Or, you can stop by their site and grab a copy for yourself.
/tip Mike Rundle on Twitter for Teehan’s review.