[animalnewbie]

I am no expert and I wish there were a start from 0 guide with examples not involving external crates but my sense is that you can write your own executor and do whatever you want. (Maybe I'm wrong?)

[steveklabnik]

You're not wrong: that is basically what this article is, and it includes writing an executor!

[nindalf]

The linked article finally helped me understand how Rust implements async. Give it a shot.