Most interesting for me was the Mojo interfaces defined at https://github.com/fuchsia-mirror/mojo/tree/master/public/in... and https://github.com/fuchsia-mirror/mojo/tree/master/services.

E.g. the application interface at https://github.com/fuchsia-mirror/mojo/blob/master/public/in...

And the framebuffer interface https://github.com/fuchsia-mirror/mojo/blob/master/services/...

I don't see any mention of a file system.