netcat

The nc (or netcat) utility is used for just about anything under the sun
involving TCP or UDP.  It can open TCP connections, send UDP packets,
listen on arbitrary TCP and UDP ports, do port scanning, and deal with
both IPv4 and IPv6.  Unlike telnet(1), nc scripts nicely, and separates
error messages onto standard error instead of sending them to standard
output, as telnet(1), does with some.

netcat was originally written by Hobbit <hobbit@avian.org> but has
recently been rewritten by Eric Jackson <ericj@monkey.org> for OpenBSD.

Current source code is available at:

	http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/nc/