There are multiple programs to make 'direct connections', but for public gaming (with a list of online servers/rooms, to play not only with known friends), since Tunngle and Evolve have closed, currently only pLan (.. OpenVpn) and gameRanger are the options.
While GameRanger currently has disadvantages like games autostarting and -closing, rooms auto-locking, amount of players being limited to one ingame-server, and strict game selection, pLan needs players a lot, please join us to play together.