Apart from logging into remote machines on the command line, OpenSSH is a versatile utility for secure networking.

Man pages

• sshd for server-side configuration
• ssh for client-side configuration

Small articles

• Authentication (client side)
  • How to use SSH Agent - Cache authentication keys
  • Authenticating with GPG (GPG agent)
• Server side
  • Restricting authorized SSH keys on the server side, to limit the access that is granted to keys stored in higher-risk places.