CurrPorts - CurrPorts displays the list of all currently opened TCP/IP and UDP ports on your local computer.
TCPView - TCPView is a Windows program that will show you detailed listings of all TCP and UDP endpoints on...
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.
TcpView For Linux - TcpView For Linux. Touch screen friendly design graphical network connections viewer for Linux.
Open Nettest - Open Nettest is a platform for collecting, processing and visualizing data related QoS and QoE.
TCPEye - TCPEye is an easy-to-use monitoring application that will display a list of all network processes.