I participated in Global Game Jam 2018, where we developed "Avis Adamis", an online multiplayer game. You find yourself in an old and rundown aircraft, trying to remain airborn. But you and your friend are under attack and must try to keep everything working. And even though you can only communicate via an old outdated "lamp-system", things get heated up quickly.
Since we only had 48 hours to develop the game, the decision to create an online multiplayer game might not have been a good one. Nevertheless, we learned a lot - I specifically had the chance to learn Unity Network programming.
I did all the network programming and multiplayer logic.