At the end of the day, your clients have to connect to a socket on a server somewhere. Either the server is in the cloud (ok, but who pays for that?), and your

At the end of the day, your clients have to connect to a socket on a server somewhere. Either the server is in the cloud (ok, but who pays for that?), and your pc has a client on it that opens a tunnel from that cloud to your pc, or they have to connect to a socket on your home ip, for which you need to open a port in your router. The only other thing that can exist, semantically, is nat hole-punching, which unless you have very good coordination with your friends can only be done through software (and also involves a server but less so). Maybe reconsider why you can't forward ports on your router? If the server isn't listening for connections on that port it's undistinguishable from a closed port, and if it is then it is available as a game server.