Not a command, but a little known feature of the Terminal app:
(shift+command+K) or Menu 'Shell' -> 'New Remote Connection...'
opens a SSH, S(FTP), TELNET connection manager window!
And sometimes handy: shift+cmd+. to toggle showing hidden (dot) files in Finder.
Sort of like command+k in the Finder, connects to a server. You can type in vnc://host or vnc://localhost:port... the latter is for VNC to hosts via an SSH tunnel.
It's quite a good VNC client, too.
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