Separate memory for the actors and communication via messages sounds like the reinvention of tasks in a classic RTOS (e.g. pSOS, Kadak AMX). Nothing C just could do, stuff which was usually done in C.

If you've never used actors to write concurrent code, you've missed out on a glorious thing. You can even do it in older languages, like C, if you use a good messaging system (like ZeroMQ). See e.g. the CZMQ library, which provides actors in C.

Actors are one of those core models every developer should know, like finite state machines.