Zerodha is India's largest stock broker with over 2 million clients and $3 billion in daily trading turnover. It has achieved tremendous scale with only 30 employees in its tech team by building its entire technology stack using open source software from the start. This has given Zerodha flexibility, avoided vendor lock-ins, and significantly reduced costs compared to proprietary software, helping it achieve profitability with no external funding or marketing. While open source allows for faster development, companies must consider all trade-offs like capabilities, quality, future costs, and inertia when choosing technologies.