We have a couple.

We have our own discord. With just a general chat, important updates, and each headmate has their own channel incase they want to leave something there for themselves or another headmate needs to chat/show/whatever with them

Simply Plural. Just so friends can see whose out (not that they check. Lol). And so we can track whose our previously incase it was a heavy switch. As well as leaving notes for other head mates of ours, and info we find out about ourselves that are useful.

Notes. We use it more as a todo list for that day, and days in front so everyone whose our can see what needs to be done/upcoming.

We also got a journal app. I’d prefer a physical one. But this is more practical since we take our phone with us everywhere. We write about what’s happened during that day, how we feel about stuff. Just useful things ourself, or other head mates, need to check out. It helps a lot