SSH (Secure Shell) is the now ubiquitous program for logging into or executing commands on a remote machine. It provides secure encrypted communications between two untrusted hosts over an insecure network, replacing the hideously insecure telnet/rlogin/rsh alternatives. Most UNIX users run the open source OpenSSH server and client. Windows users often prefer the free PuTTY client, which is also available for many mobile devices, and WinSCP. Other Windows users prefer the nice terminal-based port of OpenSSH that comes with Cygwin. There are dozens of other free and proprietary clients to consider as well.
I can't believe that this ubiquitous tools has no comment yet.
How could we live without it ?
Version 6.0 has just been released and continue to prove that OpenSSH has no real competitor in this field.