Mapforge is a self-hosted web-based GIS application for creating and sharing
geospatial data collaboratively.  Users can draw shapes, import GeoJSON/GPX/KML
files, query OpenStreetMap via the Overpass API, and edit maps together in
real time using WebSockets.

The frontend uses MapLibre GL JS with Stimulus/Hotwire.  The backend is a Ruby
on Rails application using MongoDB for storage and Redis for caching and
real-time synchronisation.  Optionally supports GitHub, Google, and
OpenStreetMap OAuth2 login.