Koichi Sasada merged the Ractor to ruby master branch (Commit). Ractor is Ruby’s Actor-like concurrent abstraction. Looks like it is going to release on RubyKaigi 2020 Takeout version (Sep. 4th, 1AM UTC).
See this thread:
I'm playing with Ractor now. Here's some observations and what not.— Richard Schneeman 🤠 Stay Inside || protest cops (@schneems) September 4, 2020
Learn more: Ractor Document.
Read this Ractors article by Brandur.