One of my first experience with open source was an old OSX app that put the Swatch time into the menubar. But it didn't work on my Mac for some reason so I downloaded the source code and Xcode then I was tinkering around (not sure I knew what I was doing) and managed to compile it and run it successfully.

Internet Time from Yellosoft https://web.archive.org/web/20080509010856/http://yellosoft....

Found a screenshot, it was a dead simple app https://i.imgur.com/yHlAlZY.jpeg

I think I still have the source code somewhere even though the original Github repo is gone. I might reupload it.