Keychain is a manager for OpenSSH, ssh.com, Sun SSH and GnuPG agents.
It acts as a front-end to the agents, allowing you to easily have one
long running agent process per system, rather than per login session.
This reduces the number of times you need to enter your passphrase from
once per new login session to once every time your local machine is rebooted.

This allows 'cron' jobs to use 'ssh' scripts in a friendly yet secure manner.
