Wikipedia
TeXShop is a free LaTeX and TeX editor and previewer for OS X. It is licensed under the GNU GPL.
It was developed by the American mathematician Richard Koch. TeXShop was modeled on NeXTstep's bundled TeXview.app and developed for the then new OS X user interface Aqua and capitalized on the native PDF support of that version of the Macintosh operating system, which was itself based on NeXTstep's successor OpenStep. Mitsuhiro Shishikura enhanced it by adding the ability to transfer mathematical expressions directly into Keynote presentations. Lacking the TeX eq -> eps Service which TeXview afforded, other apps such as LaTeXiT.app were developed to provide Service support. TeXShop requires an existing TeX installation and is currently bundled with the MacTeX distribution.
The program (then version 1.19) won the 2002 Apple Design Award of Best Mac Open Source Port for its capability to display scientific and technical documents created in TeX format. In fact, TeXShop makes it possible, thanks first to "pdfsync.sty", to switch back and forth between code and preview easily, jumping at a corresponding spot, simply by a CMD-click. From TeXShop 1.35 onward this also works with multipart documents, which are joined by "\include". Also, with version 1.35 TeXShop was extended with XeTeX support.
The Tiger version of TeXShop is capable of jumping from preview to code and vice versa without pdfsync.sty, using the PDF search technology built into Tiger.
Starting with version 2.18, TeXShop has included support for SyncTeX. This technology also allows jumping from preview to code and vice versa without including any special style file, but is much more reliable than PDF search, especially for documents that include mathematical formulae.
Version 2.26 in universal binary was released on 17 March 2009, requiring Mac OS X v. 10.4.3 or later with Mac OS X v. 10.5 recommended. Version 2.28 was released on 7 November 2009 as part of the TeX Live 2009 release of MacTeX.
For users of OS X v.10.2 and 10.3, Release 1.43 remains available (as well as v1.35e and 1.19 for 10.1.5 and earlier).
For users of OS X v.10.4 through 10.6, Release 2.47 remains available (10.5 or higher is strongly recommended).
There is a support forum, which is administered by the German project ApfelWiki.de.
A new TeXShop dock icon, designed by Thiemo Gamma, has been bundled with Release 3.39. In Finder, TeXShop documents will still use the original icon (designed by Jérôme Laurens and later re-constructed by William Adams for its use with retina displays) for associated LaTeX documents.