Good timing for me to join the community! For OP and anyone else interested: I am working on an open-source shopping list web app. It's just a web app, NOT a native Android or iOS app, at least for now.
The project is here: https://gitlab.com/jaymrosenblum/good-groceries
It's not super feature rich, I've tried to focus on usability first. The basic concepts: You have a Team with one or more Users who share a list. Users can be part of multiple Teams so you can create one-off Teams with other people for events and trips. Each Team defines one or more Stores and Sections. Each item has a few fields, a priority value (0 - Have it, 1 - Don't have it, 2 - Need it, 3 - Urgent) and can be added to multiple Stores and multiple Sections. Then when you view your list, you have controls to say which store(s) you want to view, a filter for priority value(s) of items you want to see, a keywords filter, and the ability to expand/collapse the sections. You can quickly update priorities (i.e. "check off" items) as you shop from the list view.
I'm the sole dev. But my SO and I use it and I already have a few friends and family members using it so I plan to keep improving it and keep it running as long as I can. I'm currently running the production instance on Vercel with the database on Supabase (both free tier). Anyone web dev inclined could stand up their own instance if I ever had to take mine down for any reason. And any user can take a full export of their data right from the UI at any time (currently only as JSON, but plan to add CSV option).
Integrated with google for authentication. If anyone is interested but needs an auth integration besides google, if it's supported by next-auth (https://next-auth.js.org/configuration/providers/oauth#built-in-providers) I'll be happy to look into adding it.
I have a couple updates I'd like to push out today/tomorrow before taking on new users but if anyone's interested please DM me and I'll get you added ASAP! Or reply with any questions.
p.s. I am planning to add opt-in zero-knowledge data encryption to try to address data privacy concerns, hopefully in the next couple weeks.
Glad to hear there is some interest. In case anyone comes back to this:
If anyone wants to help beta test, I opened up registration on my instance. I don't want to post the link publicly just yet but will be happy to DM it.
Working on the encryption feature now. I'm not sure yet the best way to publish updates and let people follow the progress. Open to suggestions!