Who is Quietust?
He is a member of the NESdev community who occasionally makes contributions to this wiki.
What sort of stuff has he done?
He's made a variety of things:
Where can I contact this 'Quietust' person?
Your best bet would probably be to email him (@gmail.com). He can usually also be found on Libera Chat and EFnet, generally using the nickname "_Q" (or some variant thereof), as well as on a few Discord servers.