Mac OS X
I use MagicPrefs to get rid of one-finger scrolling. Unfortunately, MagicPrefs is rather spammy in Notifications Centre. This is fixable by going into System Preferences, Notifcations, and then disabling notifications from MagicPrefs.
Don't bother installing Xcode if you don't plan to actually use the IDE to build Obj-C apps for Mac/iOS. Instead, open the terminal and type gcc and let OS X install it's own command line stuff.
If you want proper GCC rather than clang, install Homebrew then brew tap homebrew/versions and brew install gcc49.
Postgres.app is a nice way to run Postgres. If you want to run psycopg2 - the Python postgres library - add the Postgres app path to your PATH: export PATH=/Applications/Postgres93.app/Contents/MacOS/bin:$PATH before pip install psycopg2 - for RubyGem pg, see the Postgres.app documentation.