You have ETS and Mnesia that are technically shared mutable state, and people have built Raft / Paxos / DeltaCRDT / etc. which also provide some form of it -- albeit a safe one -- but while it does exist, actually sharing the state between PIDs is a very rare thing ime. I don't have super in-depth experience in the Erlang ecosystem, so take this with a pinch -- or handful! -- of salt ofc.
ETS is isomorphic with a data table process that processes get and set (and etc) messages, but happens to be quite a bit faster.
If ETS is shared mutable state, so is a process with state that accepts changes, as chrisseaton posits. Of course, shared mutable state with clear boundaries between mutations is a lot better than shared memory where everyone can write and read things in bits and pieces.
