Open Ports displays all open TCP and UPD ports using a cli (command line interface). We all know the netstat command that lists all tcp and udp connections (netstat -an). The problem with this is that it does not show the application that uses the ports listed there. Open Ports lists the applications that use the ports which makes it easier to identify applications that should not be connected to the internet at all.
The freeware requires no installation and does not change the system, just run it using the windows run command. Every user that is logged on can use the application, that´s right even guests can use it. Another great tool that uses a gui is Currports. Just follow the link if you like it.

Check Open Computer Connections With My Ports
Netstat Tutorial
Open Files Patcher
Manage Open With Programs
Does windows netstat not have the -p switch?
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 15031/mysqld
pretty handy ;)
(windows doesnt have work with -p, I just tried)
-b Displays the executable involved in creating each connection
or
-o Displays the owning process ID associated with each connection.
Works in Win2K/XP.