Does that use ractors, or plan on using ractors? Seems like it uses fibers. Is it considered the best ruby server these days?
Best server is going to vary on your preferences and workload. Puma is a great multithreaded server, and it can do fork based workers as well. But unicorn is the go to for process/fork based workers.
Falcon is newer and built on libraries that use the new fibers api.
Not sure about ractors, but the code is there, have a look
unicorn is pretty moribund. I think the maintainer has mostly moved on from ruby.