**Abstract**

Computer games and, of course, the development associated with them have been in the spotlight for many years; recently, also with technologies, such as virtual reality or extended reality. The main part of this chapter presents the classification of collaborative XR systems, the concept of the major application architectures and the consistency models of shared virtual game environments. The next subchapter briefly deals with the sharing of property ownership. The mentioned concepts and examples used in the chapter are implemented in many works and projects using a collaborative environment (also in gamified form) developed in the laboratory LIRKIS, the home laboratory of the authors. The knowledge presented in this chapter may provide tips and inspiration for some other game projects, and practical and useful notes on the advantages or disadvantages of some systems will be interesting and useful.

**Keywords:** extended reality, virtual reality, mixed reality, augmented reality, web-based collaborative environments
