Twilio on Rails Part 3 – Adding Contextual VOIP Using WebRTC to Your Rails 4 App` is a tutorial that guides developers through the process of integrating Twilio's Voice Over Internet Protocol (VOIP) capabilities with their Rails 4 applications. The tutorial covers creating a contextual VOIP experience for users by learning how to create a TwiML app, integrate the Twilio Client JS SDK, generate a Capability Token, connect the VOIP call, and dial the customer. The tutorial also includes examples of how to use the generated token to make outgoing calls and handle incoming calls in a browser-based application.