FIles via SsH, or FIles via SHell, or something like that.
A protocol for file transfers over ssh (or the like) connections, providing FTP-like abilities to browse the remote file system, create directories, etc. while needing only /bin/sh and a few other standard POSIX features to be available on the server.
Apparently rather popular in the KDE community.
A format specification can be found at [L1 ].