This application is a perfect PDF viewer that allows you to browse a large amount of PDF reference manuals, dictionary, or catalog.
The app works with the Smalltalk Class Browser and the Column Browser used in iTunes and Finder.
Instead of assigning one window for a file, it features the file pane. You can pre-register PDF files and select them from the pane on the left side of the screen for better control.
It also allows to change the title of the added PDFs, create PDFs as group or sort them.