Mentally calculating the day-of-the-week for any date in history sounds like an impossible task for a normal person, but the algorithm is actually pretty simple to learn.

Although there are tutorials for this elsewhere online, and little quizzes available, there didn't seem to be anything well optimised with multiple practice modes etc.

I originally created a basic version of this just for myself, but a small group of friends and family found it interesting and gave suggestions such as the daily game.

Multi-lingual support is a bit rudimentary at the moment, it will only translate the month names and weekday names, not other text. If any translation mistakes are identified please let me know.

Other feedback is welcome too.