Dropbox-like client for Macs to access existing FTP/WebDAV/CMIS storage We have many users on Macs that access their files on one big non-Mac server that supports FTP/WebDAV/CMIS.

PROBLEM: They can not use their files while not connected to the Internet.

QUESTION: Is there a Dropbox-like software for FTP? or WebDAV? or CMIS?


When connected, pushes local changes to the server
When connected, polls the server every n minutes to pull changes
Preferably open source
Dropbox-like UI: Tray icon, minimal configuration dialog, maybe green check in Finder to show which files are synchronized.
Starts automatically at boot or login


Just to make it clear: I am not looking for an online hosting service. I have an existing server and there are no plan to move any data to any cloud. I am looking for a client-side software that can synchronize local files with the server when connected to the network.


FTPbox is nearly perfect and open source, but it has not been ported to Mac yet.
GoodSync does not work in the background (requires user click) so it is a no-go.


I was asked to add a short section describing why DropBox is not a solution: 1) Documents are confidential, third-party is not an option 2) Dropbox is not reliable enough (better uptime/SLA is needed) 3) Dropbox becomes crazily expensive for large scale 4) The FTP/WebDAV/CMIS interface is actually provided by "Alfresco", an enterprise document management system which has many other features (not just file transfer), and is integrated with other critical enterprise systems. So my question is really about client-side only.
You may want to look into the following open source applications:


FTPSync

a Perl script to synchronize a local directory tree and a remote FTP directory tree.
ownCloud

Web services under your control. 

Current features: file management, WebDAV access, share via public link, music streaming, users &amp; groups, OpenID, LDAP
In development: sharing, encryption, calendar, contacts, etc., desktop sync client, Android &amp; webOS apps, server-server sync

NOTE: You do not have to utilize their storage.