EventMachine supports listening on UNIX domain sockets, therefore Goliath does too. Simply create a config file as per the instructions on the wiki with the following:

port = nil

This makes EventMachine take the address parameter as a unix socket, so simply run your server in the following way:

ruby hello_world.rb -sva hello_world.sock

You can then serve it up using nginx:

http {
  server {
    listen 80 default;
    location / {
      proxy_pass http://unix:///Users/boffbowsh/code/hello_world/hello_world.sock;