A Ruby on Rails Engine which provides a double entry accounting system for your application
Active Merchant is a simple payment abstraction library used in and sponsored by Shopify. It is written by Tobias Luetke, Cody Fauser, and contributors. The aim of the project is to feel natural to Ruby users and to abstract as many parts as possible away from the user to offer a consistent interface across all supported gateways.
EventMachine: fast, simple event-processing library for Ruby programs
Zohmg is a data store for aggregation of multi-dimensional time series data, built on top of Hadoop, Dumbo and HBase.