SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
The Dude - MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of the countries around the world.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
Pandora FMS - Pandora FMS: Opensource monitoring software
Packet Sender - Packet Sender can send and receive UDP, TCP, and SSL on the ports of your choosing.
cStatus - Monitor and scan a network.