What is a relay?

It is basically the same principle as vpn, tunneling connections to another net. Only you use it port for port, not all connections have to be tunneled.

Its easy to explain with an example:

We have two Users, A and B. A is running a webserver on Port 80. B is running a Firefox. Both are (of course) running tcpfile and have a working connection.

So B wants to access A's webserver. Now the normal way is to redirect the Port in the NAT, but then everyone can access A's Webserver, and not all connections to it may be encrypted. So what B instead does, he sets up tcpfile so he can connect to a local Port. TCPFile will send everything over to A. A's tcpfile connects to the apache. A just has to tell tcpfile that this is allowed for B or for everyone.

what are the advantages?

The port is not opened for everybody. The connections are all secured with the normal tcpfile encryption scheme, which means the packets are all encrypted with RSA and AES and also (g)zipped. Also, access can be set for each buddy individually.

You can even set it up so you can access another machine within the same lan.

How do i do that?

B has to add a Mapping. Tasks => Add Relay.  In the wizard, first choose the person you want as Destination.  In the next step, you have to fill out three things:

The port you will connect to on your machine.

And which IP and port it will target from A's Subnet.

A has to allow this. A opens his Settings Tab and goes to Connections => Allowed Relays. There he can add a specific port or even a range of ports which all people are allowed to access.

A can also set it for each person individually, which ports and IPs may be accessed. For that he goes to View => Show User Settings => (B's Name). In the spawning tab he will be able to override the global settings and add Ports only for this person.

 What has been tested?

 So far we have only tested webserver and vnc. But basically any Client/Server model over TCP where you can configure the client to connect to a different port should work.  UDP is not supported currently.