18 April 2009: I've updated the chart and added 2collab, the “Read” category, sharing of PDF files, and the Mendeley bookmarklet and full-text search.
15 July 2009: I've updated the chart to indicate that Mendeley and Labmeeting have integrated PDF viewers and that 2collab can search Scopus.
20 July 2009: I've added the offline version of RefWorks for Windows, EndNote OpenOffice plugin, and full-text search in several tools.
22 February 2010: Many small changes, including a few more categories. Added Citavi and dropped 2collab, LabMeeting, and Connotea.
6 August 2010: Added Mendeley API and iPhone app, EndNote X4 features.
19 September 2010: Moved chart to different location, PDF download, Creative Commons license.