Author sounds nice, but it resembles creative work (writing, painting, ..).
Creator maybe?
Is there some more agreed-upon "title" for people with decent side-projects which are still "side" and not founded companies?
Thanks
Look at all of the titles in your job history and re-word them into descriptive labels if necessary. "Senior Programmer" works across organizations, "Code Wrangler II" does not. Titles don't have any consistent meaning in the programming field.
If you want to call out work done outside of an organization describe it in clear language: open source contributor, side project, hobby project, etc.
Some employers may see side projects as a negative. They might wonder if you will just take a job to finance a startup, or work on your side projects on their time or with their resources. I suggest thinking through that possibility and only presenting side projects if they have some relevance to the job, and you can assure the potential employer you won't use their time to do your own thing, or quit as soon as you get a few paying customers for the side gig.
In my case I would prominently feature my side projects to showcase my capabilities, discoveries, and potential. Nobody cares.
What’s important is your employment history, years of relevant experience, and percentage match to the criteria of the current roll. It’s not about how good you are but well you fit. The better of a developer you are might actually work against you. If you have a lot of side projects, like I do, and have invested substantial effort to advance your capabilities, as I have, I am sure you will find that supremely depressing.
Always remember the goal is employment, not craftsmanship.