I don't see why you disqualify SSH here. If you want a system that only deals with filesystem operations, I suggest NFS. It is neither firewall-, NAT-, proxy- or browser-friendly, is not cross-platform (Windows support only if you pay extra) and is neither encrypted nor authenticated. But hey, it deals with filesystem operations only.
If, on the other hand, you want a system that meets your last 3 requirements, just use SSH/SFTP.
It's straightforward to permit SSH access but not shell logins.... if you can administer user and group settings. I guess stuff like scponly (http://freecode.com/projects/scponly) is useless if you're running Windows server-side.
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I don't see why you disqualify SSH here. If you want a system that only deals with filesystem operations, I suggest NFS. It is neither firewall-, NAT-, proxy- or browser-friendly, is not cross-platform (Windows support only if you pay extra) and is neither encrypted nor authenticated. But hey, it deals with filesystem operations only.
If, on the other hand, you want a system that meets your last 3 requirements, just use SSH/SFTP.
SSH is a pain to secure properly, and the potential for mischief is huge. There is no sudo in FTP.
It's straightforward to permit SSH access but not shell logins.... if you can administer user and group settings. I guess stuff like scponly (http://freecode.com/projects/scponly) is useless if you're running Windows server-side.
Not that I'd like to encourage it, but there could be a sudo in FTP, along the lines of WU-FTPd's infamous support for a "SITE EXEC" command.