Sidekiq

A high-performance background job processing framework for Ruby that handles millions of jobs per day for thousands of companies worldwide. Created by Mike Perham as an open-source project in 2012, it grew through an open-core model offering a free community edition alongside paid Pro and Enterprise tiers with advanced features like rate limiting, batching, and unique jobs. Built and maintained largely as a solo operation, the business generates approximately $580k per month in subscription revenue, making it one of the most successful independently run developer tools in the Ruby ecosystem.