The author here. I can understand that it's not clear from the README, but I only chose a Rack implementation for the backend in order to make developing those

The author here. I can understand that it's not clear from the README, but I only chose a Rack implementation for the backend in order to make developing those 'Adapters' easier for others, since Rack is pretty standard in the Ruby world. One of the implemented adapters, Proxy, acts a proxy to another HTTP server. In the performance section: "[The results] show the power that lies in the simple addition of a SPDY server to an existing nginx/Thin configuration (and probably also Unicorn/nginx.)" I am totally for the separation of front- and backend.