rails-disco (rubygems):     Rails Disco is a framework that extends Rails with support for the best parts of event sourcing.      Instead of updating models synchronously in Rails, these changes are captured in commands. Commands are validated in a domain and create the only source of truth: events. Later events can be projected into Rails models and other actions.      Have a look at the documentation on Github for more details. 
Keywords: distributed-systems|event-driven|event-sourcing|framework|ruby