I would like to generate HTML Snapshots using Watir, hosted on Heroku.
Google\'s Full Specification for Making AJAX
Troelskin's answer is incorrect. There are ways to run "headless" browsers with Watir, which do not require a "full desktop environment". Having said that, I do not know which method may be appropriate on Heroku.
Other "headless" automation options (if you are using Ruby) are Mechanize with Open-Uri, along with (optional) Nokogiri.