If you're a new Mac user, check out this list of cool Mac apps installed by default.
- Automator - an awesome application to automate repetitive tasks. The icon is of a robot, which I don't understand why people don't click this awesome looking icon. It's surprising how little this is used, considering how awesome it is. Use this! It can save so much time.
- Emacs games - this is quite hidden, but if you thought Chess was the only game available in OS X, you're wrong. Just open Terminal (in /Applications/Utilities/Terminal) and type in "emacs" without quotes. Then, press enter, then Esc and X at the same time. Yes, Esc. Type "tetris", press enter and enjoy. There are loads of other games included in the Emacs program.
- Archives.prefPane - just a simple prefPane to change settings of Archive Utility.app in the System Preferences. You can change this by navigating to /System/Library/CoreServices, then opening Archive Utility.app, but this prefPane should really be included in the System Preferences app. But just navigate to /System/Library/CoreServices, right click Archive Utility.app and select "Show Package Contents". Navigate into Contents/Resources and double click Archives.prefpane.