RailsAdmin is a Rails engine that provides an easy-to-use interface
Doorkeeper is an OAuth 2 provider for Ruby on Rails / Grape
Object-based searching
Track changes to your rails models
A Rails engine that helps you put together an admin dashboard
Simple, efficient background processing for Ruby
A performance dashboard for Postgres
Coherence is a full featured, configurable authentication system
Better error page for Rack apps
An open source search engine with RESTFul API and crawlers