Today it's hard to imagine web products not linked to popular services. Our Ruby On Rails developers have implemented a bunch of different integrations, e.g. social networks(Facebook, Twitter), payment systems (Paypal, Stripe, Braintree), geo services (Foursquare, Google Maps/Places, Yahoo Local, Yelp, etc.), email marketing (Sendgrid, Mailchimp), business tools (LinkedIn, Zendesk, Pivotal Tracker), etc.
While integrating, we do not only use 3rd party API’s, but also build our own API’s that can be used by third party applications.