I instructs my Apple friend to get Sshfs, i.e. to mount an outside target, to home -directory but he cannot find sshfs for Mac. Dose there exist some substitute or some Apple-compiled version for Sshfs? If it exists, how can my friend install it?
You can get sshfs with MacPorts. Just download macports and run
sudo port install sshfs
in a terminal window.
Harald suggested a package-installer but some alerts: package-installers such as MacPorts and Homebrew have problems such as old packages and broken packages. For example, the Homebrew's Sshfs is broken at the time of writing. Package-installers contain MacPorts and Homebrew here. You may be interested in this thread here. It is better to find the newest installation so you won't face odd errors. For example, the Sshfs -development files are here and the packages here.