DEVONagent [OS X]

DEVONagent is a metasearch tool that downloads each of the primary search results and analyses their text to categorise and pick out the best results. It's made by the same people who make DEVONthink. I mention it here because of the PubMed plugin, which allows you to search biomedical abstracts in a similar manner to Scirus, but faster and on your own desktop.