Should run on Heroku, as is.
This is a very very barebones example of a custom web app using the Adafruit IO Ruby client, Sinatra, a smidgen of jQuery to exchange data with Adafruit IO, and enough caching to prevent hammering your account limits.
NOTE: If you build a site like this and open it to the public, you'll probably exceed your API limit pretty quick :| Caching helps a lot.
$ git clone https://github.com/abachman/adafruit-io-shared-client.git
$ cd adafruit-io-shared-client
$ heroku create
$ heroku config:add IO_USERNAME=yourusername
$ heroku config:add IO_KEY=yourkey
$ git push heroku master