nc - arbitrary TCP and UDP connections and listens

File transfer between machines:

    $ nc -l 1234 > filename.out

Using a second machine, connect to the listening nc process, feeding it the file which is to be transferred:

    $ nc host.example.com 1234 < filename.in

Or a simple web server:

    $ while true ; do nc -l -p 1500 -c 'echo -e "HTTP/1.1 200 OK\n\n $(date)"'; done