antirez made dump1090. mutability forked it and made it a lot better. dump1090-mutability became dump1090-fa when mutability started working for FA. dump1090-fa was forked to readsb by Mictronic. Independently wiedehopf forked dump1090-fa webinterface into tar1090 (to originally work with dump1090-fa as a backend mainly). Then 2019 wiedehopf forked readsb and started working on making it scale to more than 500 planes using tar1090 as a webinterface.

Now wiedehopf readsb fork can handle aggregating from > 10k users. It can track all the planes in the world at once and serve API requests at scale. tar1090 can work with that readsb fork API to get data for the current viewport. Server side the readsb API is very CPU efficient so that usually the server limit will be bandwidth or load balancer (of your choice) requests per second. This should make it (relatively) simple for anyone to aggregate ADS-B data and serve a global map using open source components.