TeXShop is a TeX previewer for OS X, written in Cocoa. Since PDF is a native file format on OS X, TeXShop uses "pdftex" and "pdflatex"; rather than "tex" and "latex" to typeset; these programs in the standard teTeX distribution of TeX produce PDF output instead of DVI output.
TeXShop uses TeX Live, a standard distribution of Tex programs maintained by the TeX Users Group (TUG) for Mac OS X, Windows, Linux, and various other Unix machines. The distribution includes tex, latex, dvips, tex fonts, cyrillic fonts, and virtually all other programs and supporting files commonly used in the TeX world. The most recent version of this distribution is maintained for the Mac by the MacTeX TeXnical Working Group of the TeX Users Group and available under the "Obtaining" tab.
The latest TeXShop release, version 3, requires System 10.7 (Lion). An earlier version of TeXShop, version 2, is also maintained and requires System 10.4 (Tiger), although System 10.5 (Leopard) is strongly recommended because it fixes several important bugs in Apple's PDFKit code, extensively used in TeXShop. Users with systems 10.2 or 10.3 should use TeXShop 1.43, and users with systems 10.0 and 10.1 should use TeXShop 1.19. Both of these versions are available on this site.
TeXShop is distributed under the GPL public license, and thus free.
Updated on Jun 16 2022
TeXShop 4.75 changed the behavior of Preview in "double page" and "double-multipage" modes. This proved to be controversial and is fixed in version 4.76. If your default display environment is "multipage", none of these changes matter to you. TeXShop uses Apple's PDFKit to display pdf files. This kit has two properties named "displaysRTL" and "displaysAsBook" which change double page behavior. Both are booleans. Most scripts are written from left to right, and setting displaysRTL to NO causes the pages to also flow from left to right. Scripts like Arabic and Hebrew are written from right to left and setting displaysRTL to YES causes the pages to also flow from right to left. In TeXShop 4.75, the "Page One on Left" and "Page One on Right" preferences set this property. This also holds for 4.76, but the items are renamed "Pages Flow Left to Right" and "Pages Flow Right to Left."
Version 4.75 ignored displaysAsBook, although earlier versions usually set it to YES. When it is YES, the first page is shown by itself and the remaining pages are shown as double pages. By convention, there are an odd number of pages in a book before the actual content begins, so this causes the left and right pages to appear as they would if a user opened the actual book.
In version 4.76, displaysAsBook is set to YES by default and the initial page appears by itself. Just in case, a hidden preference setting named "DisplayAsBook" is included, and users who dislike the single page can get rid of it by issuing the following command in Terminal:
defaults write TeXShop DisplayAsBook NO