What you are looking for is local peer-to-peer file sharing. When I was studying, we used eMule, but that is for Windows and old. I don’t have a concrete software suggestion, but looking around the gnutella protocol could be promising.

Edit: QuantumCogs suggestion is also good, the use cases are slightly different.

Probably any “cosy game”. If I remember correctly there is a community on Lemmy.

Oh wow. I remember trying to play this as a kid for 2 hours or so. Since then I occasionally thought about it, because the concept is interesting, but could not remember the name.

Now I can check it out again.

No, basically all licenses in the family are pooled together. You own game A and B, you can play game A, someone else game B. There are 2 licenses of game A in the family, two people can play it at the same time.