ITexMac
Crowd-sourced documentation and tutorials by the Cocoa developer community
"iTeXMac is an integrated software which components are: - a text editor dedicated to D.E. Knuth's TeX typesetting system - a frontend to a teTeX like distribution, that includes TeX engines and tools - a PDF viewer"
See http://itexmac.sourceforge.net/ an ugly page which belies the fact that this is an active project with excellent use of cocoa and integration with the OS's PDF services.
