Skim is an open-source PDF reader. It is notably the first free software PDF reader for Mac OS X.  It is written in Objective-C, and uses Cocoa APIs. It is released under a BSD license. It is also cited as being able to help annotate and read scientific papers.
Its primary release was in April 2007 at version 0.2. Within its first year it managed to gain a small fan base of users due to its ease of use and features which allowed some flexibility over other PDF browsers for Mac OS X. As of 2008 it had achieved version 1.0. Its main developers were also responsible for another popular open-source program, BibDesk.
Some of its features include the ability to view and bookmark PDFs, highlight and underline selectable PDF text, and a Full Screen and Presentation mode. It also allows the adding of circles and boxes, as well as being able to embed and edit notes.
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