I was previously a happy user of the popular menstrual tracker app, Clue, which was pretty gender-neutral and not too fertility-focused while storing all its data on the user end. Lately, however, Clue added more paid services and started to pester me more and more often to upgrade, not just with a fee for a paid version, but to a monthly subscription. And then on top of that it stopped working unless you create an online account, so I promptly uninstalled it.
I happened to find a completely not-for-profit, transparent and open-source alternate called drip., which doesn't have any accounts or store user data and doesn't even have a paid version. Unfortunately the interface isn't as customizable, so I can't remove the buttons for fertility-related stuff that I don't want to track (and that kind of gross me out, although I'm on the fence wrt if I should feel bad about that). Still, that's pretty minor. And since it's open source, I could always learn how to code and do it myself.
I happened to find a completely not-for-profit, transparent and open-source alternate called drip., which doesn't have any accounts or store user data and doesn't even have a paid version. Unfortunately the interface isn't as customizable, so I can't remove the buttons for fertility-related stuff that I don't want to track (and that kind of gross me out, although I'm on the fence wrt if I should feel bad about that). Still, that's pretty minor. And since it's open source, I could always learn how to code and do it myself.