HistoryBook 
HistoryBook is a ruby implementation of the event sourcing pattern.
This library provides an interface for event sourcing over a pluggable back end data store. Currently it supports the Sequel gem and its data stores as well as an in-memory data store for testing.
Usage
To run the example below you will need to install (or place in your Gemfile) both the sequel gem and the pg gem.
HistoryBook.configure(:sequel) do |config|
config.connection_string = 'postgres://localhost/history_book'
end
HistoryBook.open('test_id') do |stream|
stream << HistoryBook::Event.new(:customer_created, :name => 'Joe Tester', :address => '100 West Washington')
stream.commit
end
HistoryBook.open('test_id') do |stream|
stream.events.each do |event|
puts "Playback event #{event.type} with #{event.data.inspect}"
end
end