We are Ruby On Rails experts, Building products would not be possible without knowledge and extensive usage of many other things, e.g. Angular/Backbone JS, NodeJS, Realtime Pub/Sub, Redis, NginX, PostgreSQL, AWS, Heroku and many more.
Mobile application development is a term used to denote the act or process by which application software is developed for handheld devices, such as personal digital assistants, enterprise digital assistants or mobile phones.
The back-end of an application is responsible for things like calculations, business logic, database interactions, and performance. Most of the code that is required to make an application work will be done on the back-end.
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, payment systems (Paypal, Stripe, Braintree), etc.