Activity Monitor
What It Does: This utility shows you how much processing power, memory, disk and network activity your Mac is currently using.

When You Use It: Use Activity Monitor to see if an application or process is eating up too many resources and causing your Mac to become sluggish. If an application or process is using up a lot of processing power, you might need to restart the application or possibly your computer. If a program or resource is using most of your available memory, it may be time to get more memory.

Audio MIDI Setup
What It Does: This controls audio input and output on your Mac.

When You Use It: To fine-tune audio settings and connect MIDI-compatible devices such as musical instruments to your Mac.

Bluetooth File Exchange
What It Does: Allows you to send files from your computer using Bluetooth.

When You Use It: To send a file such as an image or music file to a Bluetooth enabled device such as another computer or your cell phone. You’ll only see this utility if your Mac has a Bluetooth adapter.

Boot Camp Assistant
What It Does: Sets up your Mac for booting into Microsoft Windows.

When You Use It: To run Microsoft Windows on your Mac. This will walk you through setting it up. You’ll need a full copy of Windows to install, an Intel-based Mac and Mac OS X 10.5 Leopard. This allows you to choose between Mac OS X and Windows when starting your Machine. Third-party alternatives include Parallels and VMware.

ColorSync Utility
What It Does: Manages color information across different devices such as scanners, printers, monitors, etc.

When You Use It: If you are a professional graphics designer you’re likely already using this. Monitors, printers and scanners all handle color differently. ColorSync was invented to make sure the color synchronized. There is not much here for the casual user.

Console
What It Does: Displays messages sent between applications and your computer.

When You Use It: This is for programmers and technical support. It is used to help debug and solve problems. Unless you’re one of the above, there is not much to see.

DigitalColor Meter
What It Does: Displays the color value for any pixel you select on your screen.

When You Use It: Graphic designers use this to quickly sample a particular color on their screen without having to use a special image editing program such as Adobe Photoshop.

Directory / Directory Utility
What They Do: Provides shared information about people and resources within an organization across a network.

When You Use It: If you are in an office that has a directory server, you can access shared contact information, email groups and more. This is convenient to keep everyone in the office in sync. Directory manages this information while the Directory Utility helps you connect. New in Mac OS X 10.5 Leopard.

Disk Utility
What It Does: A lot. Verifies and repairs your hard disks, creates disk images, erases disks, repairs system permissions, burns discs and more.

When You Use It: Anytime you want to do any of the above. This is one of those essential utilities and probably the one you’ll use most. If your system is acting up you can try repairing disk permissions (opinions on the effectiveness is hotly debated). If you suspect a problem with your hard drive (internal or external), you can repair it. You can burn writable media such as CD-R and DVD-R. My personal favorite is making a disk image of software that requires the CD. Just make a disk image of it and mount it before starting the program. No need to fumble around for the CD.

Grab
What It Does: Makes screen captures of windows, menus and more.

When You Use It: A great utility that has been predominantly overlooked. Command-Shift 3 & 4 are great, but Grab gives you more control. The most helpful is probably the Timed Screen Capture option that enables you to capture menus and more. You can also access Grab from the Services menu of just about any application.

Grapher
What It Does: A full-function graphing calculator.

When You Use It: To make graphs based on simple or complex equations. Great for people into mathematics and/or for making cool-looking graphs.

Keychain Access
What It Does: Stores and protects passwords to applications, web sites, email, servers and more.

When You Use It: Anytime you tell your Mac to remember a user name and password. This unassuming little application is infinitely helpful when you can’t remember your login information to something. As long as you can remember the password for your Mac, you can access the rest here.

Migration Assistant
What It Does: Transfers user accounts, applications and more from one Mac to another.

When You Use It: Most frequently this is used when you are upgrading from one Mac to another and want to transfer your files, settings and applications to the new Mac. But you can use it at any time. You can also use it to transfer information from a Time Machine backup.

Network Utility
What It Does: Provides detailed information about your Mac’s networking.

When You Use It: To access networking information such as IP address, adapter, and more. You can use Network Utility to “Ping” another computer, lookup Whois information, Finger and more. If you are knowledgeable about networking, it is invaluable to help troubleshoot issues.

ODBC Administrator
What It Does: Administers databases and applications that use the Open Database Connectivity standard.

When You Use It: Database administrators use this to connect to applications like Filemaker to databases.

Podcast Capture
What It Does: Records and distribute podcasts.

When You Use It: Podcasters use this utility to connect to a Mac OS X Server with Podcast Producer. It offers advanced features for creating and uploading podcasts. Available only with Mac OS X 10.5 Leopard.

RAID Utility
What It Does: Administers RAID (Redundant Array of Independent Disks) set ups. RAID is term for data storage that divides or replicates data across multiple hard drives.

When You Use It: If you employ RAID storage techniques you will use this utility to create and monitor your RAID. Requires a RAID card and drives.

System Profiler
What It Does: Provides you with everything you need to know (and more) about your Mac.

When You Use It: Anytime you (or technical support) wants to know something specific about your Mac. Find out what brand of hard drive or optical drive you have, what is connected to your Mac via USB, Memory and much much more.

Terminal
What It Does: Provides direct access to the UNIX underpinnings of OS X.

When You Use It: If you need to access parts of OS X that weren’t designed to be easily accessed. The Terminal wields a lot of power, but if you’re not careful, you could inadvertently do a lot of damage.

VoiceOver Utility
What It Does: A screen reader that announces what appears on your screen. It speaks the text in documents and windows.

When You Use It: Developed for persons with visual impairments, it actually reads aloud what is displayed on screen. It also supports Braille displays.

X11
What It Does: Runs UNIX tools and environments.

When You Use It: For people who know UNIX, this utility will let you run the many UNIX tools that are based on the X Window System graphical user interface. This utility is not always installed by default so if you have a need and don’t see it, run the Mac OS X install disk and select it from the customize menu.