Ralley is described as 'Simple, robust message queue as a service, that requires absolutely no setup as it works over HTTPS!'. There are five alternatives to Ralley for a variety of platforms, including Windows, Linux, Mac, Online / Web-based and Self-Hosted solutions. The best alternative is RabbitMQ, which is both free and Open Source. Other great apps like Ralley are ActiveMQ (Free, Open Source), sidekiq (Freemium, Open Source), Celery: Distributed Task Queue (Free, Open Source) and Amazon SQS (Simple Queue Service) (Free).
Simple, efficient background processing for Ruby. Sidekiq uses threads to handle many jobs at the same time in the same process. It does not require Rails but will integrate tightly with Rails to make background processing dead simple.