ServerTalk is an application that allows you to communicate directly with an open TCP or UDP port on a machine. It is similar to a graphical Telnet client, but lets you pick the port, and lets you use TCP or UDP. This can be very useful for low-level troubleshooting of server issues when using any of the clear-text based protocols such as FTP, Telnet, HTTP, etc. Also a great learning tool.
Download: ServerTalk 1.0