Netcat is a networking utility providing access to outbound and inbound connections, TCP or UDP, to or from any ports. It has built-in port-scanning capabilities, with randomiser, and advanced usage options, such as buffered send-mode (one line every N seconds), and hexdump (to
stderr or to a specified file) of transmitted and received data. It also features a tunnelling mode which allows special tunnelling such as UDP to TCP, with the possibility of specifying all network parameters: source port/interface, listening port/interface, and allowing the remote host to connect to the tunnel.
Particularly re-useful in this context are its capabilities for port scanning, transferring files, port listening, and that it can be used as a backdoor.
Ncat was written for the Nmap Project as a much-improved reimplementation of the venerable Netcat. Ncat is integrated with Nmap and is available in the standard Nmap download packages (including source code and Linux, Windows, and Mac binaries) available from the Nmap download page.