We looked at a few options including httpcommander
In the end we used Microsoft Unified Access Gateway. We lost the WebDAV functionality, but kept the web interface and permissions model.
NetStorage runs your login script in the background, this allows it to bring your mapped drives to the web interface. If you went with an FTP solution you would need to find a way to replicate that.
I would like to basically replicate the functionality of http://www.element-it.com/asp-net-explorer-browser/online-share/web-file-manager.aspx
where a webpage will display the windows file shares the logged in user has access to. Someone told me that it was possible but I cant seem to figure how