|Gnome vfs layer||3||C Library||UNIX||LGPL||Used by e.g. Nautilus|
|Paramiko||3||Python Module||LGPL||Used by e.g. Bazaar|
|sshj||1-3||Java API||Java||Apache License 2.0|
|OpenSSH||3||UNIX||BSD||Widespread in the UNIX world|
|mod_sftp for ProFTPD||1-6||UNIX||GPL|
|Green End SFTP Server||3-6||UNIX||GPL||Still under development|
SFTP is a network protocol, usually run as an SSH subsystem, that provides file transfer operations. It is not (at the time of writing) fully standardized but is nonetheless widely implemented. It is not inherently tied to SSH but is usually used that way.
SFTP is not FTP over secure transport.
A wrapper in this context is a program that does not implement the SFTP protocol itself but just invokes some other client to do the work. While this doesn't make them any less useful for users the distinction is worth making from an implementor's point of view, as there is not much point doing interoperability testing against wrappers if you've already tested the underlying client.
(Most SFTP clients don't implement SSH themselves but call some separate SSH client to do that job. Again from an SSH implementor's point of view this makes them relatively interesting but from an SFTP implementor's or user's point of view the distinction is usually pretty academic.)
Please contact me if you know of any implementations not listed above. Please include:
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