XOS is now packaged as a project in the larger CORD open source initiative, with source code managed through https://gerrit.opencord.org. It is also mirrored at:
https://github.com/opencordHttps://github.com/open-cloudthe latter of which corresponds to the configuration of XOS we run on OpenCloud.
Up-to-date information about XOS is available at the CORD Wiki. Additional information is available at the original XOS web site, but it is now somewhat dated.
The best way to get started with XOS is to bring up a "Single Node CORD POD," as described here. This version is configured with a service graph that includes ExampleService, which is a good platform for understanding how to build and use XOS.