Heroku is a pure platform as a service -- that is, the entire infrastructure is managed by Heroku and not by you. As such, deploying a Ruby application, whether or not it is Rails based, is practically effortless. Deployment, in fact, is performed as a part of a regular SCM (software configuration management) sync via Git, an innovative, freely available, and quite popular distributed source code management system pioneered by Linus Torvalds, the creator of Linux.
Via Heroku's tight Git integration, there are no extra steps to publish code live. A developer simply executes a Git push of committed code to a Heroku repository, and the platform takes care of the rest, from downloading required dependencies (via Bundler) to scaling out the target application per the application's setting.
Scalability in Heroku is achieved via the platform's notion of dynos and workers, which are computing resource units. The more dynos or workers, the greater the number of incoming requests the application can handle simultaneously. Lastly, Heroku's price point is easy: An application with one dyno is free. You incur a price only when you add computing resourcing, such as extra dynos.