CurrPorts - CurrPorts displays the list of all currently opened TCP/IP and UDP ports on your local computer.
PortsMonitor - PortsMonitor is a system utility for monitoring system TCP/IP network connections by application...
TCPView - TCPView is a Windows program that will show you detailed listings of all TCP and UDP endpoints on...
Total Network Monitor - Total Network Monitor is a network monitoring software that is designed to continuously monitor your local network, individual computers, and services. Free for 60 days.
Port Checker - Check open ports online
Netactview - Graphical network connections viewer for linux