If you're interested in code I write, explore it on GitHub. Usually, it will be under at least a MIT license, so do with it what you want (while you follow the license). I might be able to provide support, but don't count on it.
I used to develop for macOS. I don't do anymore, but some of my apps are still around somehow and I happen to get support requests from time to time. As I don't use a Mac on a daily basis today, I cannot build or support these apps anymore. Consequently, I have removed those apps that were available in the Mac App Store from it. Nevertheless, feel invited to have your own go and build and use the code. You'll need to have a Mac, obviously, Xcode, and the source code from below links. The apps might not build out of the box.
Monotony was a simple RSS feed reader app for macOS. It displayed new feed entries as desktop notifications, using either the macOS notification center or Growl. Monotony was available in the Mac App Store for some time, but is now retired. Its source code is available on GitHub.
Recent Menu monitors changes happening to files and folders on your Mac in real time, including custom filters and contextual actions. Recent Menu was available in the Mac App Store for some time, but is now retired. Its source code is available on GitHub.
Recent Redux monitors changes happening to files and folders on your Mac in real time, including custom filters and contextual actions. Recent Redux was the first app I developed and published in the then Mac App Store, back in March 2011. It is now retired, but its source code is available on GitHub.
A macOS application to synchronize bookmarks between different desktop browsers. Get the source code on GitHub.
Cocoa classes for having fun with Mountain Lion's Notification Center, as well as a sample app. Get the source code on GitHub.