This is some software available for Mac OS X that can be useful. Note that applications downloaded from 3rd party sources can contain malware. Using the App Store is safe, but avoid other sites that host apps. Try to make sure you download from the creator of the product, not a 3rd party.
The first thing you want to do for Mac OS X is make sure XCode is installed. This can be done from the App Store. If you install Homebrew (below) then it will install XCode for you when it finds you don't have it.
Package Management System
The next thing you'll need is a package management system for Mac OS X. This basically enables the installation of Unix packages on the Mac. There are two for Mac, Homebrew and MacPorts. I prefer Homebrew.
LaTex
MacTex - This package includes the Latex distribution plus TexShop, Bibdesk, LatexiT, etc.
TexLive - This is an option on a Windows machine. The editor TexStudio has been suggested by some.
Text Editors
Emacs - A very versatile text editor, good for coding since it has syntax highlighting.
Terminals
iTerm - This is a great little terminal program for Mac OS X. The main feature it adds is better cut and paste.
Python
Python likely comes with your computer; however, it is often useful to install your own copy which can make many things run smoother. Easy ways to do this are to your Homebrew, or install Anaconda Python or yt.