<p>Several approaches have been proposed in the past for conducting conceptual modeling and model-driven engineering using virtual or augmented reality. However, traditional metamodeling platforms only considered 2D environments and did not natively integrate three-dimensional representations. This limits the possibilities for experimentation and research in this emerging field. Therefore, we present in this paper the web-based MM-AR metamodeling platform. It combines conceptual modeling in traditional 2D environments with the creation and manipulation of models in 3D space. MM-AR is based on a modern technology stack and natively provides support for the WebXR device API, which permits to run virtual and augmented reality applications in a web browser without additional plugins. In addition to a description of the conceptual and technical architecture of MM-AR, we demonstrate the platform’s capabilities through two use case scenarios. The first scenario includes the realization of traditional modeling languages, whereas the second scenario demonstrates how the platform was used for realizing a no-code solution for creating augmented reality applications using the Augmented Reality Workflow Modeling Language (ARWFML). The platform is provided as open-source project on GitHub.</p>