Multiplayer Interactions in a Singleplayer

Clarification

Here a singleplayer game has some way to interact with the singleplayer worlds of other players.

Example

X4: Foundations has the ability to send cargo ships to the game world of other players. This is somewhat similar to how Animal Crossing does multiplayer, there you can visit the islands of other players.

These interactions are often characterized by simply sending small amount of data. Players can't interact with the game world of other too much. I.e. they don't have the same options as in their own world.