There's also companies that create open source projects and go on to build highly differentiated value-add products on top of it. E.g. Databricks (owners of Apache Spark) who built a great SaaS product for managing data science pipelines. That product is so valuable it's almost as if they don't even need to monetize the spark project by itself.

What I don't like is the companies that create some open source project for the hype, then charge for a 'management console' or some marginal add-on.