This website really does only one thing, though it does it very well. It makes a PDF file smaller. This can be useful if, say, you have a large PDF file that you need to email to someone, or perhaps you have a large collection of files which you don't want to get rid of but which is taking up a lot of space on your hard disk. The system is entirely web-based, so there's nothing to install. Just visit the site and drag a file from your desktop to the browser. Once the file is uploaded, it'll be converted straight away, and you can then download the new version.
Shrink Link: http://compress.smallpdf.com/