Most shared to-do apps make you choose: one list you both live in, or two lists nobody else can see. Neither fits a couple very well. You don't need your partner scrolling past your work reminders and dentist notes, but "who's booking the plumber" really shouldn't live in a text thread that both of you forget about.
Here each of you keeps your own To-Do List, and any task can be marked as a household task. A household task is given to one of you or to Anyone, with a due date if it has one, and it shows up in the To-Do of whoever it's for, on the right day. Either of you can tick it off, edit it or hand it over, and the other sees the change within moments, with who did it. Everything else on your lists stays private. To be straight about the tiers: whoever creates the household needs a Premium plan and the other person needs Basic or higher; the to-do list on its own is free. If there are kids in the picture, the family chore list page shows how chores work for them too.