I've never heard of an FTP server with any capabilities that are even vaguely CGI-like.

I remember some embedded device that could get a firmware update via FTP (FTP upload to a special name). That's quite common, you can do that with many printservers and other embedded devices. But that device could also be rebooted by writing to another special name.

I suppose you could (very) roughly approximate it by having a directory where users can upload a text file containing a request and a cron job which checks that directory for request files and, if it finds any, processes the request and writes an output file, which the user can then download.

inotify, dnotify, and other filesystem notification systems should be more efficient than a cron job.

But I doubt you're likely to get much closer than that without using a heavily-patched server (and probably a customized client as well) to add the CGI-like features.

You could also make the ftp server access a FUSE filesystem to implement tons of magic in that filesystem. And you could get the same magic via NFS or Samba as well.

Plus, there is also a (mandatory) SITE command in FTP, that can implement site-specific commands. Several FTP servers implement SITE EXEC <command> to run an external executable. SITE CHMOD is also quite common.

Alexander