I use nextcloud tasks and deck for keeping track of things. Tasks is great for checklists, calendar integration, reminders, etc., I use it for simple reminders like trash day, and things I don’t want to bother with making a calendar event for. You can have it make a calendar event, but I don’t. Deck is a kanban style thing with calendar integration as well, it’s a bit more job-task oriented so I use it to help me juggle tasks when I have a lot of projects that need keeping up with. Setting up nextcloud is way overkill for just those features, though. If you’re not looking for the other features of nextcloud, I don’t think it’d be worth it.

It is pretty easy to set up if you go the nextcloudpi route on Debian, you don’t need a raspberry pi. Any computer running Debian can do it, but you may need to install a few dependencies if you’re on minimal Debian that aren’t listed anywhere, at least last time I set it up they weren’t. But again, if you aren’t looking to use the rest of nextcloud, I wouldn’t go that route.

If your floorboards are visible in the ceiling you’ll want to put up some drywall or something on the ceiling, every time someone walks on the floor above, some dust will get knocked loose and fall from the ceiling. You could put up some drop cloths as well for a quicker, less permanent solution.