Looking for a To-do list app

Hi friends. I'm looking to replace as many Google services as I can from my life and I am currently looking for a Google Keep alternative.

I want something extremely basic, like Google Keep, that just allows me to collaboratively create to-do lists. Me and my SO have a bunch of to-do lists such as shopping, house chores or work related tasks. I want to be able to share lists with her.

I've tried a bunch of apps suggested by some friends but honestly they're more geared to creating documents or elaborate notes. That's not what I want. I just want to create to-do lists and an interface that allows me to do that as simply as possible.

Thanks!