I was reading Richard Downer's excellent response about how Amiga libraries work and one sentence in particular got my attention:
Yes, a pointer to exec.library is always at $4, and this is (in theory, but not in practice) the only fixed address you should ever use in AmigaOS.
I only ever knew about $4! So what are other addresses/data in a fixed memory location in AmigaOS?
(Of course, I'm not talking about hardware registers; this question is specifically about software related addresses and memory areas)