Nestled within the bosom of your Mac's system folder lie many powerful and curious applications. Not intended for direct access, the denizens of the CoreServices directory work as clients for other OS apps such as System Preferences or Safari. There are several CoreServices apps we use often at TUAW. Here are some of our favorites.
When Safari cannot connect to the Internet, you may be prompted to run Network Diagnostics.app to find the problem. The app lets you choose a network port you wish to work with (Ethernet, Wi-Fi, or an external modem), and test it. It is one of many apps found inside your /System/Library/CoreServices folder. It's also one that you may want to stick into your dock for a bit when you're messing around with a new router or have upgraded your cable modem.
Screen Sharing.app gives you remote access to any enabled computer on your local network using the VNC protocol. Some of us prefer using Chicken of the VNC, but Screen Sharing.app is a simple alternative already built into your system.
You enable this feature in System Preferences > Sharing > Screen Sharing (hint, click Computer Settings and add a password). When launched, just enter the host name or address of a sharable computer (e.g. Banana.local or 192.168.0.15) and start controlling that system remotely.
Use the Wi-Fi Diagnostics.app to capture network events and enable debugging logs. It provides a way to collect traffic for analysis.
Anyone who regularly works with Apple development may be pleased to realize they can access the Certificate Assistant.app directly instead of always having to launch the Keychain utility. The assistant allows you to create certificate signing requests, which are used in the dev process to request authenticated items like certificates for development provisions.
The VoiceOver.app utility enables spoken descriptions of your OS X screen. It provides an audio interface for your computer. Once enabled, you can quickly switch out of VoiceOver mode with Command-F5. (You can turn on VoiceOver via System Preferences/Accessibility, as well.
You're probably used to using the Archive Utility.app through the Finder's contextual pop-up, but if you drag it into your dock, you can use it as a drag and drop compression utility. Very handy!
Got other favorite secret apps? Tell us about them in the comments!