Skim is a PDF reading and note-taking app for Mac OS X that is designed to make reading research papers and manuals better. Just like in Preview, you can search, scan, and zoom through PDFs, but you also get some custom features for your workflow: Snapshots If thereРІР‚в„ўs a graph on page two and the description continues to page three, just draw a box around the graph with the command key down and a snapshot window pops up with the graph, and you can keep on reading with the graph in view. For more fun, minimize that snapshot window - they stick around in their own dock in the document window. Tooltips If a PDF has links, such as for citation references or indexes and section headings, you can click on them as usual to go to the destination, but thereРІР‚в„ўs more - hover the mouse over those links and Skim will show you a tooltip with the target of the link. No more losing your place to peek at a citation! For more fun, command-click on a link to pop up a snapshot window showing the linkРІР‚в„ўs destination. Presentation and Full-screen Modes Full-screen reading is handy. So is showing a PDF as a presentation. But theyРІР‚в„ўre a little different. For instance, you might not want to show the table of contents in a presentation, but itРІР‚в„ўs nice to see it when youРІР‚в„ўre just reading by yourself. So Full-screen and Presentation are separate modes in Skim.