- netcat-traditional http://www.stearns.org/nc/
- netcat-openbsd : https://github.com/openbsd/src/blob/master/usr.bin/nc/netcat... (also packaged in Debian)
- ncat https://nmap.org/ncat/
- netcat GNU: https://netcat.sourceforge.net/ (quite rare)
To prevent any confusion, I like to recommend socat: http://www.dest-unreach.org/socat/