Offering a virtual toolbox of ten Internet utilities, IPNetMonitor allows Mac users to monitor virtually every aspect of their network connection. Sure, you'd expect to find tools like these in the Utility folder of a network administrator, but they'll also come in handy on the average person's Mac.
IPNetMonitor includes DHCP lease, a useful tool for anyone with a DHCP connection to the Internet. It tells you when your IP address was assigned and when it will expire. The suite also includes Connection List, which shows you which ports are open on your machine, and who is connected to them. Also useful is the Port Scan application, which scans any IP address for open ports. Granted, this type of tool is usually for hackers and the like, but it can come in handy on your own network to help find holes that may need filling (or in this case, closing).
The toolbox doesn't end there, though. The suite also includes useful Internet tools such as Ping, Trace Route, NS Lookup, Who Is and Finger, as well as a subnet calculator (handy if you're starting to configure a network, say, behind a router and want to figure out what your subnet should be with the number of machines you have). The tools work without a lot of intervention on your part, so you don't have to be a pro to use them effectively.
Some of these tools are already included in the OS X beta, so certainly a set of tools such as this may have an uncertain future. However, if you want to know what's going on with your network right now, you should take a look at IPNetMonitor.