As you already noticed nearly everything is possible with OSM - because our raw data is *free*. If you like to just view the standard OSM map you could use a local application which shows the tiles. If you use a Linux PC: You can misuse our top editor https://wiki.openstreetmap.org/wiki/JOSM for that (hey, (just do two clicks and display the OSM Carto map as background layer; hey, and maybe you even like to contribute to OSM ...). JOSM is FOSS and written in Java. However, if you would like to inspect the code there are surely muuuuch more lightweight software which just displays a pre-made map. See https://wiki.openstreetmap.org/wiki/Software/Desktop .

As you already noticed nearly everything is possible with OSM - because our raw data is *free*. If you like to just view the standard OSM map you could use a local application which shows the tiles. If you use a Linux PC: You can misuse our top editor https://wiki.openstreetmap.org/wiki/JOSM for that (hey, and maybe you even like to contribute to OSM ...). JOSM is FOSS and written in Java. However, if you would like to inspect the code there are surely muuuuch more lightweight software which just displays a pre-made map. See https://wiki.openstreetmap.org/wiki/Software/Desktop .