TCPView - TCPView is a Windows program that will show you detailed listings of all TCP and UDP endpoints on...
Proc Net Monitor - SecurityXploded is an Infosec Research Organization offering 200+ FREE Security/Password Recovery Tools, latest Research Articles and FREE Training on Reversing/Malware Analysis
Fping (open source) - fping is a program to send ICMP echo probes to network hosts, similar to ping, but much better performing when pinging multiple hosts.
CurrPorts - CurrPorts displays the list of all currently opened TCP/IP and UDP ports on your local computer.
Open Nettest - Open Nettest is a platform for collecting, processing and visualizing data related QoS and QoE.
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.