How do I get the player count of another server/place?

If both places are within the same universe, you can use DataStores, if the places are in different universes your best bet would be using HTTPService. If you use HTTPService you could get that information two different ways, the first being if you own the game you're trying to get the player count from and the second being if you don't own it. The first would be to have the game you're getting the player count from POST its current player count to an external server and have the game receiving the player count GET the player count. The second method is having an external server check and store the player count retrieved from the game page and have game GET it from the server. Both of the HTTPService methods require some amount of programming on the server side. Nothing much, probably some simple PHP or Python.

If my answer solved your problem please don't forget to accept it.