Look under the picture at the top of this blog. Those white words are links to other pages of this blog. Check out the Popular Downloads page to see a list of free applications you can download and install on your Mac. The latest addition to the list is Skim, a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file.
Have you found any cool or useful free apps for your Mac? Mention them in the comments and I will add them to the list.