**2. Classification of collaborative XR systems according to availability**

User collaboration is significantly affected by the availability of systems that provide a shared virtual environment. In fact, the availability of collaborative virtual environment systems is classified according to the local or global access of users/players, as well as their physical or remote (virtual) presence.

Collaborative XR systems are divided depending on availability into the following categories:


Each of these categories has specific properties related to user access to the target system, the sharing of users' interactions, and the resources needed for a possible gaming environment implementation.
