Cloud-X uses Google Cloud Print to share files between different users and devices. Along with the PC and Android app the Java API to access Google Cloud Print is also released.
This is a very early version, so there might be bugs.
The Android app and an online and stand alone PC version can be found at the following site:
UpdateThe website is no longer online.
API with included sources can be downloaded from http://fun2code.de/downloads/GoogleCloudPrint.jar.