This thread is very old, but
https://obs.ninja/ works again. I am unaffiliated with OBS, but I was the creator of OBS.ninja and I finally set it up to work again. Only took an end-of-the-world pandemic for me to have time to work on it again.
It is a fairly simple tool, totally free, and purpose built for OBS. It just uses WebRTC to bring in low-latency video from another computer or mobile into OBS via the OBS Browser Source element. I've started re-building it from the ground up, so some of the original features are still missing. I'll have it probably fully done by end of week.
I use it for my own personal needs, like for using my iPhone as an OBS webcam or for group hangouts on OBS, but feel free to use it for whatever. Code is easy to read if interested.