What is used as a backend on multi-streaming (restream) services, such as: restream, switchboard, goodgame, etc. for RTMP relay?

Question

Nginx

I would like to raise my own server for relaying without transcoding the rtmp stream to several different services according to the scheme: OBS / XSplit, that is, rtmp output -> Restream server -> Twitch, YouTube, GoodGame, etc.
Everywhere it is suggested to use Nginx with the rtmp module, the option is clear and tested, besides it absolutely does not require resources, but it is interesting what is used (theoretically it can be used) for similar purposes on large and popular platforms that relay the rtmp stream?
From a technical point of view, what can be done to relay an rtmp stream to several resources? ffmpeg?

Answer 1

gg - nginx-rtmp
Those who have many good developers write their own