I programmed in Ruby and Rails for quite a long time, and then I fell in love with the simplicity of the Sinatra framework which allowed me to build one page web application
You may want to take a look at Axiom (disclosure: it's my own project). It is largely inspired by Sinatra, built on top of Cowboy and offers a lot of the features, Sinatra does.
-module(my_app).
-export([start/0, handle/3]).
start() ->
axiom:start(?MODULE).
handle('GET', [<<"hi">>], _Request) ->
<<"Hello world!">>.
This handles GET /hi
and returns Hello World!
.
Take a look at the README for a documentation of it's features.