Back in 2013 I was in a Facebook group called Game Maker Hungary (you should not join, it is a very bad community). There was a guy who made some android games, and I tried them out. If I found a bug I wrote about to him. Some day he asked me if I would like to create a game. He had a concrete plan. I accepted the offer and made my first commit on 2013-12-06.
This was my first big homework in the University. It was made under a week in C and with SDL2. It had to be smaller than 1MB if zipped, with all the images, sources, and documentation. It works on Windows, Linux, and it (should) run on Mac too. It has a limited map set, but with the built-in editor it can be expanded any time by the user. (Levels can be shared with a little trick.