Does anyone know what technology is used to providing streaming? Both in terms of the broadcaster and the viewers. There doesn't seem to be any big open source projects in this space from what I can tell.

Check out nginx-rtmp [1] and ffserver [2] (from the ffmpeg team).

[1]: https://github.com/arut/nginx-rtmp-module

[2]: https://www.ffmpeg.org/ffserver.html