GemNofitier is a web app that help rubyists to keep updates on latest gems what they subscribed.
It's hosting at http://gemnotifier.org/
Notes: the project need two parts setup
hook up with rubygems.org http://guides.rubygems.org/rubygems-org-api/#webhook the controller handles the hook is hooks_controller
run cron task to send updates mail, you need to specify your mail setting in production.rb cron.rake
Submit issues: https://github.com/intridea/gemnotifier/issues