Unfortunately, openvpn. :/

As you know, OpenVPN cannot do what n2n can do.

Someone has to run an OpenVPN server. Everyone on the network has to trust that server.

And connections between network participants are not peer to peer.

With OpenVPN and most other VPN's, if I'm not mistaken, each person's traffic passes through a central point: some VPN server/appliance.

This is a major difference and has its own set of security implications.