GoToMyPC allows bidirectional communication between the client (any browser) and a host computer. The host computer can be behind a router and still be accessible to the client anywhere on the internet. This is done despite the fact that no router port-forwarding rules exist.

As I understand it, the host computer stays in contact with GTMPC servers and when a client connects to GTMPC, the GTMPC servers pass along the connection info to the client to permit direct communication (or something to that effect).

Let's say I wanted to allow bidirectional communication between an internet client and a host computer behind a router without having to configure port-forwarding on the router. What are the options to accomplish something like this?