Transporter [amazon.com] feels almost like dropbox, but is a physical device you have to plug somewhere into your network. Folders on your machine are going to be synchronized automatically with the transporter. You can choose whether you would like to keep a local copy or access the remote files directly.
You can even keep multiple transporters, which synchronize the data in P2P fashion.
The main difference to dropbox is the data location. Transporter is you device and your data is stored on a replaceable hard disk and your own private cloud.
About four years ago, I wondered Will Moores Law Kill Public Clouds?. There are still public clouds out there :-), but cheap hardware and technologies like KVM, VMWare, or XEN bundled with automation, make a private cloud interesting.
The only caveat of private clouds is power and bandwidth. Because of higher density, centralized computing is more efficient, than decentralized devices. However, Transporter is a low power device and could be competitive with commercial, public cloud storage offerings.
No idea, whether Transporter uses Java somewhere, or not :-)