@wwwonka, hopefully our expert @yannick can offer some insight on this 
I read briefly through the second repo webrtc-without-signaling-server. It seems this demo did not require a signaling server, since the caller (user creating offer) and callee (user answering offer) both live on the same web browser index.html page. This would not work in either peer-to-peer or client-server situations. I think some form of signaling (some options being HTTP requests as mentioned by yannick, WebSocket, or even by pigeon mail 
) is required for both of these scenarios.