And if you know enough about how to operate your router you could just simply go to your router's panel, enter your local IP, enter FreeSO's port and it would just work without messing with your OS.
See, it leads to nowhere. Port forwarding is all about letting your router know that this specific PC is the one that hosts the service (in this case, FSO server). And no, you don't need to install any weird thing LRB is suggesting.
It won't leave you without internet connection if you do something wrong, it won't compromise your security (it's not like a THIRD PARTY FAKE LAN DRIVER that connects your computer to a virtual LAN network), it will be easier for everyone to connect to your server (does Hamachi still have 10 peers per room limit?), there is no way you would share more than you want to and if you ever got BSOD, you have one third-party driver less to worry about.
Just sayin', we could just spend another month or two on this Hamachi vs port forwarding debate and won't get to any meaningful conclusions. You could now say that Hamachi kind of stuff is easier to setup, sometimes you can't do port-forwarding because you can't access your routers panel etc. and - yes, sure. And Tunngle is also designed in a way that enables you to have a game lobby, with chat, games list etc. And yes, you could even integrate FreeSO and Tunngle on the code level to provide some of this in game itself.
But I still think people actually don't like installing things just to play online on a server for... let's say, less than hour. When I see that something requires this kind of software, I'm like - okay, too lazy to do that, whatever. I've never had Hamachi installed for more than few hours and setting it up always felt like a waste of time.
