## 2 Related Work
**Creating and deploying web-applications--**Regarding web-applications creation and deployment, a recent set of standards advocated by the Google Web Fundamentals group introduced features such as offline support, background synchronisation, and home-screen installation [25]. Such an approach is known as _Progressive Web-Applications_ (PWA) that aims to offer responsive, connectivity independent, app-like, discoverable and linkable web-based solutions. PWAs have completely brought in a new dimension to mobile development, making web apps look, feel and act similar to native and hybrid apps [26]. Web-applications (including those dealing with interactive 3D content) can be deployed in local or networked contexts in order to be consumed by final users. _Node.js_ ([[https://nodejs.org/](https://nodejs.org/)]([https://nodejs.org/](https://nodejs.org/)), accessed on 22 November 2021) is an open-source, cross-platform, back-end javascript runtime that allows to build scalable network applications [27]: it's often employed for deploying web-applications, including those targeting Cultural Heritage field [24; 28; 29; 30]. It is common in Node.js contexts to offer also REST APIs [31] to perform server-side tasks or allow easy integration with external services or platforms. Furthermore, _microservices_ emerged as a new architectural approach, in which distributed applications are broken up into small independently deployable services, each running in its own process and communicating through lightweight mechanisms [32]. These approaches allow us to design robust web-oriented frameworks with modular architectures, easily adaptable to a wide range of requirements and hardware (small servers up to large infrastructures) with the possibility to independently control service components. **Collaborative Web3D--**There is indeed a strong interest in the literature for CVE (Collaborative Virtual Environments) widely investigated for desktop-based applications [33; 34; 35]. The possibility to share the same virtual 3D space and interact with other people, became even more appealing during the COVID-19 pandemic [36]. Most of the recent literature is focused on social VR [37] paradigm, which is gaining more and more attention on desktop-based applications. There is already a robust literature on taxonomy [38] supporting the design of these applications, alongside user experience [39] and highlighting opportunities for CH [40]. Several works are also focusing on the importance of avatar representations [41] within social VR, and investigations related to personal spaces [42]. Within Web3D/WebXR contexts, there are a few works investigating synchronous collaboration, in which multiple users access the same virtual (immersive) space using common web browsers [43]. The most prominent example in the open-source panorama is certainly _Mozilla Hubs_ ([[https://hubs.mozilla.com/](https://hubs.mozilla.com/)]([https://hubs.mozilla.com/](https://hubs.mozilla.com/)), accessed on 22 November 2021) (based on A-Frame) that allows users to create online virtual meeting spaces, and it's being used also for live workshops with children [44]. Recent research is also investigating multi-user collaboration through decentralized approaches for live coding environments in WebXR [45]. Regarding proprietary solutions, _LearnBrite_ ([[https://www2.learnbrite.com/](https://www2.learnbrite.com/)]([https://www2.learnbrite.com/](https://www2.learnbrite.com/)), accessed on 22 November 2021) is another collaborative web-based solution focused on micro-learning and instructor led training, allowing to create shared immersive scenarios across multiple devices. From a technical perspective, real-time communications are typically realized through web-socket protocol [46], often adopted for creating multi-player WebGL games [47] and 360 social VR experiences on the web [48].