The integration of Building Information Modeling (BIM), or Historic BIM (HBIM), and Geographic Information Systems (GIS) has assumed a crucial role not only in the management of smart cities or urban districts, as well as in the construction sector or infrastructures but also in the management, conservation and safeguarding of cultural heritage. This integration opens up new opportunities for decision-makers to assess the impact of interventions on heritage sites, evaluate preservation strategies, and facilitate informed decision-making processes. This contribution presents and describes the open-source web platform developed within the Interreg MAIN10ANCE project. The project aims to promote a common methodology for the cooperation and collaboration of the various stakeholders involved in the restoration, management and maintenance activities of built and cultural heritage sites. This objective has been pursued by creating a BIM-GIS database, focused on the definition of planned maintenance activities, whose data has been made available to professionals and management bodies by means of a shared web platform, usable directly in situ on a tablet or portable devices. The paper highlights the key components of the web platform, including the BIM, GIS, and artifact Viewers, the Planner, and the overall Dashboard. The platform's multiscale and multi-source approach makes it extensible to various cultural assets, whether environmental, architectural, or movable. By integrating historical and geometric information and planning maintenance activities, the web platform thus supports public administrations and professionals, amending existing state-of-the-art solutions.