Soon I am going to start the next side project. Because I am going to learn Java I want to learn by practice networking. And it may be game or some kind of network tool.
Some time ago I have created solo and with my team few a few synchronous and asynchronous multiplayer games on WebSockets with Phaser and Unity to learn gamedev patterns, so I know good multiplayer is hard to create but I prefer done than perfect. ;)
Anyway, what type of multiplayer game you recommend? Simple RPG? Fighting? Racing? Flying? I will pick one idea and eventually create a simple and open-source game based on it.