SSH is the descendant of rsh and rlogin, which are non-encrypted programs for remote shell logins. Rsh and rlogin, like telnet, have a long lineage but now are outdated and insecure. However, these ...

Is there a program more commonly used in day-to-day Linux computing than SSH? I doubt it. Not only is it rock-solid, secure and versatile, but it also is extremely simple to use and feature-rich.