With Zapier you can easily create (almost) custom integration between a bunch of web apps - but not Marketo 😞
Add Marketo and there would be a bunch of exiting integration just waiting around the corner. Event apps such as Eventbrite and Meetup. More examples include Drupal, Disqus, Wordpress, Twitter, Facebook incl. Pages, SurveyMonkey, well a bunch and also webhooks, emails, smtp, rss.