SSH or Secure Shell is most well known by Linux users, but has a great deal that it can be used for. SSH is designed to create a secure tunnel between devices, whether that be systems, switches, thermostats, toasters, etc. SSH also has a unique ability to tunnel other programs through it, similar in concept to a VPN so even insecure programs or programs running across unsecure connections can be used in a secure state if configured correctly. SSH runs over TCP port 22.