Build widely-adopted open source libraries to create a permanent traffic funnel for commercial products
Create free, MIT-licensed open source tools that become industry standards. Once they achieve millions of downloads and deep adoption by major companies, use their documentation and ecosystem as a distribution channel to funnel developers toward your commercial product that solves the next-level problem.
When to use
When you have deep technical expertise in a domain and can build a genuinely useful free tool that developers will adopt widely before creating the commercial product on top
Don't do this
Building a mediocre open source tool purely for marketing rather than genuine utility - developers detect and reject self-serving open source projects
1 Founder Who Did This
Built Nodemailer (7M+ weekly npm downloads) as a free MIT-licensed library used by Microsoft, Apple, Mozilla. Documentation pages link to EmailEngine, driving 66% of its 6K monthly visitors. Also created ImapFlow as MIT-licensed feeder library generating additional traffic.