Out of curiousity, I visited one of the sites just now and was able to download a random book from one of the links provided. That said, the first set of links for the book didn’t work.

That’s a really good way of reframing things, I like it.

Periodical is great menstrual cycle tracker.

It’s opensource and available on F-droid, plus the calendar can be backed up to SD or wherever and imported back into app.