Most of the more advanced users know that Windows can do a netstat command just like on linux. And this provides you with all the connections currently on your system. This allows you to take a look at what applications might be accessing what ports and from what IP addresses. ConnectionWatcher does the same, except it takes that data and puts it in a nice neat little GUI so you don’t have to scroll around in a commandline window.
It’s a great little tool for those that aren’t familiar with commandline or just don’t want to deal with it. Another thing that’s beautiful about this, is that not only does it look at incoming and outgoing, but it actually marks what application is creating the network streams that are going out. That gives you a really easy way to review if you’ve been compromised and if a process shuts down cleanly or if it just waits for a timeout or what. This even works with Vista now!
A more in-depth look at ConnectionWatcher at freewarejunkie.