The most popular implementations of netcat are:
While all serve the same purpose, they differ in feature richness.
Has a feature, that allows it to be used to execute a command with post data from STDIN. That makes netcat a good standalone server and more versatile than nc.
port scan with nc
nc -z host.example.com 20-30
send a mail with nc
As copied from its man page:
nc localhost 25 << EOF HELO host.example.com MAIL FROM:<email@example.com> RCPT TO:<firstname.lastname@example.org> DATA Body of email. . QUIT EOF