I have heard about hamachi, but what I was thinking about is something different. When you have two computers connected to the same local network (Same router) you do not need any port forwarding or fancy tools. You simply use the local ipv4 address of the computer you try to connect to. Your OS will have some tool for finding this address (ipconfig on windows, ifconfig on linux). For example, all computers connected to the same router as me can reach my computer at 10.0.0.89. This will not work with your friends on a different local network, but it is a good way of testing if the game actually works.