JBossCache can be used as a replicated cache, and WebDAV provides a filesystem-like interface to it so it can be accessed using any WebDAV-capable client, including Windows Explorer.
With DavCache you get a simple distributed filesystem, just drag and drop a file into a mounted DavCache folder and it will be instantly replicated across the cluster.
Additionally, it can be used as the foundation for a Content Management System. A very simple CMS example is included with the distribution.
DavCache integrates especially well with JBoss, but you can use it in any servlet container or application server.
More documentation can be found on the Wiki.
DavCache is distributed under the terms of the LGPL.