What it is: A PDF manager—think iPhoto for PDF, but with superior tagging, and no weakness for mucking about with file locations.
Why it’s good: Along with being absurdly fast (our copy was ready to rock on a Mac with several thousand PDFs after about two seconds), Yep automatically creates tag keywords based on document locations, and, unlike iLife apps, doesn’t copy documents into its own database—it just leaves them wherever you’ve stored them. User-defined tags and smart collections enable you to rapidly create virtual dynamic groups of PDFs based on your own criteria, and since metadata is written to each file, searches can be performed in Spotlight. The ‘Tracking Locations’ sidebar enables you to navigate in a Finder-like way, but filters the main view to display previews of PDFs in the current folder and nested ones. Also, the succinct manual’s dead good and should get you going if you find the interface a wee bit bewildering to start with.
Where to get it: Yep is available from Ironic Software, costs $34, and requires Mac OS X 10.4.10 or later.