My first job was working for Sendmail, Inc. Their entire business model was based on helping people configure open source Sendmail, via consulting and/or a commercial web UI for configuring the software. And of course selling support for the open source software.

And it wasn't even intentional. The software existed for almost two decades before the commercial company. The commercial company sprang up because the open source authors needed paychecks for all the support they were doing. And also a bunch of companies were selling Sendmail consulting. So they figured people would rather buy consulting from the people who actually make the software.

Sadly, it didn't work out. The company was acquired for a loss to the investors.