Vassal is not exactly what you are asking for (not web based for example) and it does not generate maps or counters, you have to create your own and import them

Vassal is not exactly what you are asking for (not web based for example) and it does not generate maps or counters, you have to create your own and import them. But it does allow players to share a screen, move counters, and play a game over internet. This is known by most wargamers, so my apologies if I am pointing out the obvious,. https://vassalengine.org/ https://vassalengine.org/