WebRTC handles the actual p2p audio and video, but has no method of signaling the other party for attention to actually join the "call", -- no concept of userid

WebRTC handles the actual p2p audio and video, but has no method of signaling the other party for attention to actually join the "call", -- no concept of userid, so you'd always need to send a link to your WebRTC service via another channel - SMS, WhatsApp, Email, IRC, ... or some other "new" service, that's really just a wrapper to handle the userid / notification problem, and uses WebRTC underneath.