[ixkkglhg] Connecting two computers

Wirelessly connect two computers in proximity without need of an additional switch.  Motivation is multiplayer game.

Nowadays we really we want it between smartphones.

Let it work in isolation (neither has internet), but also work if both are on internet, but not interfering with either's connection.  The latter might make implementing this over wifi nontrivial if the "main" internet is already using the wifi, perhaps hogging every address.

Bluetooth?

The problem is as old, but still not solved!