There's hundreds of continuous integration systems out there, enough to learn from and build your own. Even if you have a product that is truly a snowflake, there's a lot of other ways to go about handling this. Maybe they tried to go about this a different way, for some reason I doubt it. Here's a few other ways this could have been handled:
- Talk to the employee about their open source implementation. Maybe there are some things you can bring back to your product from their open source implementation and pay the developer to work on doing it.
- Realize that the employee seems to have passion about this product and figure out how to elevate them into a more important role.
- Talk to the developer about how we can make open source a big part of our business model (I notice appendTo has some open source projects already) and offer to put them in a role getting paid to work on their project so long as the repo goes under the appendTo organization on GitHub, or the developer gives a shoutout to appendTo on the project, blog posts, conferences, etc.