Slippy Maps

When Google Maps first came out these kinds of maps used to be called "slippy maps" because you can just click anywhere and drag the map around, and it will continuously make network calls and load more tiles of the map that were previously offscreen as you drag them on. The same is true as you zoom in and out - it has cached tiles that fill out the map area with different detail at different zoom levels, and as you zoom it makes network calls bringing back tiles for the new zoom level. It does all of this automatically based on it's source code.

In the 2 screenshots below, you can see that 2 separate network calls were made, to bring back 2 tiles of the map that are showing seamlessly in the app's map:

The main open source version of a slippy map that caught on and everyone used was Leaflet. It is still developed, but new versions come out slowly.

Then Mapbox GL JS came out and got popular and was originally open source. Eventually it stopped adding open source updates. People took the final open source version of Mapbox GL JS and kept developing it and releasing new versions, and that open source offshoot is Maplibre GJ JS.