Network Utility in OS X is an useful application that allows you to do things such as port scans, traceroute, ping and get network interface information.
If you are using OS X Mavericks, and have used Network Utility before, you have now probably noticed that it is not in Utilities folder anymore.
Location of Network Utility has been changed to /System/Library/CoreServices/Applications/.
You can launch the application from here, or you can create an alias and copy it to Applications folder.
Read more about Network Utility on Apple support page.