Comment by cryptonector

To this day the single most successful open source business model is the SQLite Consortium's. Their approach is to make the codebase open source (public domain even) and the test suite proprietary. Having a fantastic test suite that is proprietary acts to blunt the community's ability to fork the project, and it encourages those who want new features to pay for consortium membership because the team can't easily accept outside contributions (because in order to do so the team has to write tests for those outside contributions). It's brilliant!