NetLimiter

NetLimiter is a software product from Locktime Software. It's focused on simplicity and ease to use.

As a matter of fact, it was a very fast download (about 500k), and after a few seconds I could install it.
With this simple program, you can detect which program is opening connections to which ports, in order to keep an eye on your ongoing and ingoing traffic, and sometimes to know which ports are needed to run which applications.
At the first moment, a wizard comes to the screen, detecting the networks registered on your PC (IP ranges) and that's where you have to assign them to a specific 'zone': local or Internet. Thus, the traffic statistics can be correctly separated in the statistics module (only available in the pro version).
In the main window, you can see the process list with their connections, with the ability for set a speed limit. Moreover, you can set a few options for the program like the connection speed.
One important thing to know is that in the author's site, the reviewed version of this software (1.3) is old: the latest version of this product is 2.0.10, however you can still download the old version and even buy it.