- Generally ports should work, but GameMaker is known to have obscure platform-specific bugs. There are also some functions (mainly the ones dealing with the file system) that only work on Windows or Mac.
- You should be able to test online with 2 windows on the same machine if you do it in this order:
1. Open the game exe. Set the "Target Port" to a different number. I usually use 63567. 2. Open another game exe. Set the "Ingoing Port" to the same number. 3. On the first game, do "Join with IP" and type in your local IP address. 4. Accept the join request on the second game.