There is close to zero. Sun describe the Sun Ray 2 as:
Sun Ray virtual display clients are simple, low-cost, low-power devices that require no desktop administration. Unlike complex Microsoft Windows or Embedded Linux-based thin clients and PCs, Sun Ray clients do not need to be upgraded when new applications are introduced or more computing power is required. Users can access their sessions from any Sun Ray client on a local area network (LAN) or wide area network (WAN). With a smart card, a user simply inserts it into any available Sun Ray client and instantaneously accesses an existing session.
There is nothing to configure on the terminal.
I haven't tried it out but Google found me an open source java-based server (jOpenRay) that supports the Sun Ray 2. The source was released in July 2010 and, at the time of writing (June 2012), there appears to have been no further updates to the jOpenRay website.
Any comments? email me. Last update June 2012