I don't think it's open source but we use our groceries. Just links to an email only no password. They just send you a code when you link the email to a new app. It's also cross platform if that matters at all. Also requires no permissions granted to run and only requests a camera permission to scan barcodes.

Google play link

Vikunja (hosted on tchncs: https://todo.tchncs.de/) is great for tasks but I haven't tried using it for a grocery list.