Marvin Felder, Founder of Calenso, talks about scaling his online scheduling solution to 100K users worldwide. He discusses the challenges of staying bootstrapped, adapting to enterprise customers' needs, and the importance of knowledge-sharing in the founder community. They also touch on the significance of attending events and exploring what others are doing. Other topics include rebranding, expanding to European and US markets, managing a larger company, security compliance, and using FOMO and analytics for marketing strategy.