Just checked out both drip and Bluemoon, both FOSS from F-Droid with local only data

Bluemoon lets you import data from Flo, but to export data from Flo, you need to make an account with Flo, it seems. (It also let's you import data from Clue, but I don't use Clue.)

drip lets you import data just from a CSV file, nothing that seems specific to any app format. So far I like drip a lot better, TBH; the UI is more intuitive to me, and it seems more featureful. Its prediction also lines up with Flo after putting in data since January.

However, I have just downloaded both apps. My plan is to keep Flo around for one more cycle while I compare it to the others, then kick Flo to the curb for becoming enshittified spyware, with sad nostalgia for the life-changing product it originally was to me.

Right now, I am not seeing luteal vs. follicular phase estimated with just period data on either, though, which is annoying. I want a rough sense for the purposes of some tailored nutritional stuff, but I'm not looking to get pregnant or anything and really do not wish to bother with the trouble of taking daily temperatures. Flo currently gives me that. I know it's basically just adding 15 days but I still like having the at a glance feature.

EDIT: Adding Mensinator, another FOSS one on F-Droid, to the trial. Looks like this one offers an import feature, but I have no idea what format it's expecting, because it couldn't find my export from Bluemoon. Mensinator does provide the option to just mark a day as ovulation, which neither Bluemoon nor drip offer. It does at least seem like drip tells you if you're in the first or second half of your cycle on the individual day profile for the day of, but I want something I can use for meal planning. Mensinator may be the best suited for me so far, but I will give them all time.

Also, bafflingly, when I attempted to export my data from drip, it provided me a "share file" option to share the .csv file without a simple option to just...download it.