Google has two cloud offerings - Compute Engine and App Engine. Compute Engine is an infrastructure-as-a-service setup (think AWS, Digital Ocean, etc etc etc) that provides a VM that you can run anything you want on. App Engine is a platform-as-a-service setup (more like Heroku) where you only upload your application code and the rest is handled internally by the service.
More details here:
There were some efforts at making Rack and Rails apps deployable on App Engine by using the Java support with JRuby, but the project appears to be abandoned (last updated 2011 or so).
--Matt Jones