You can use it to access and modify the files and directories on your server via FTP or direct file access.
eXtplorer runs natively under Joomla! 1.0 - 3.1 and can also be used as a standalone app.
I hope there is some sort of supports from the developer or at least a clear instruction on installation process in Readme.txt.
I am also now using the standalone script (link removed) and it is indeed the solution we were all waiting for when hosts do not have a Filemanager.