I'm looking for a simple application which will do something like
Signing up for the account should be online. The upload doesn't have to be FTP, in fact I would be happy with a web based tool which supported upload via some sort of java applet or something similar. I don't care about what platform it runs on, it will end up on a dedicated VM. Any ideas?
Well, for the actual fileserver, WebDAV would probably make sense.
It is well-supported on most desktop systems, and standardized. There are many free servers available.
For the "ask for account" part: The simplest thing would be to have a webpage with a mailto: link. Let the user send an email asking for the account, then create it manually.
If you want something more integrated, you'll probably have to implement it yourself. I don't know of any software to do this automatically.
You could probably use some kind of hosting frontend, which ISPs use for administrating their customer's server, but that would be significantly more complicated & heavyweight than what you want, so might not be a good fit. That really depends on your exact requirements.
We use the PHP webapp w2box for a similar purpose. It doesn't support multiple users out of the box but perhaps you can code a small authentication module with separate directories per user (I started coding this once but ended up just using .htaccess and separate w2box installs due to lack of time).
