Calendar Generator is just a personal experiment for exploring procedural generation of calendars and astrological events that are compatible with the physical properties of the planet.
Said that, contributions are always welcome. You can fix bugs, help in input robustness, make the webpage look nicer and ask for new features.
If you are working on small tasks, just make a pullrequest. If you want to work on a bigger task, then open an issue first so that I (and other people) know that you are working on it.