In the beginning, there were separate internets. By Postel's law, it is hard to stop them converging into one, though [1]
Your last question, though is more about "Are there alternate networked information systems than WWW"? Gopher is still active [2]. Gemini is a proposed modern incarnation of Gopher [3]. There is also Alfi [4]. There seem to be run by hobyists, though.
If there are any other comparable platforms, I'd like to know too.
[1] https://apenwarr.ca/log/20200708
[2] https://cheapskatesguide.org/articles/gopherspace.html