kip is one of the few applications to take a real stab at helping you organize all your documents, both digital and 'real world'. It combines the look and feel of iPhoto with the real world aggregate paradigm of Delicious Library, then tosses in some really slick tagging and .Mac syncing features for that finishing shine. On the left is a dynamically scaling tag cloud that keeps track of all the tags you've used on all documents. Mouse over it and smaller tags will scale up in size to help you read them better. Mouse over a document (as you see in the screenshot) and a live preview of that section of the document is displayed next to your mouse. Documents can be viewed from within kip or opened externally via Preview.
The 'real world' aspect enters the scene when kip's scan function is used, as this app wants to help you organize all your documents, including those receipts and old tax returns that are just decomposing in a box somewhere.
One of the drawbacks I've found after poking around with kip is that it seems very focused in the kinds of files it will accept. It takes picture files and PDFs, but not text files or (not surprisingly) Word docs. Overall though, this is a clever app with a nice implementation. It offers a lot of handy methods for storing all sorts of metadata, including author and URL, and seems to be one of the first i-app-like applications to do tagging well (hint hint, Apple!).
This initial version of kip is free, but as its product site plainly states: the next version will require the purchase of a license, with the price TBD. Grab a copy while it's hot, and free!