EspoCRM, an open-source CRM application for small and mid-size businesses, has seen an average of over 16,000 downloads per year and makes up to $30k per month, offering efficient tools to systematize customer data, improve sales cycles, and automate routine administrative tasks.

Solo founder Todd Hooper bootstrapped Prerender.io from zero to $2.5 million in ARR over 5 years by releasing an open-source project on Github and turning it into an SEO-friendly version of React, Angular, and Javascript websites, and then offering it as a SaaS service for businesses.