It's literally called Half Price. Updates every Wednesday morning with the colesworth specials filtered to your location (and you can have either only one or both supermarkets in the list), categorised by product type eg frozen, household, pantry etc. You can save items for that week to create a list. Idk how to get it to bookmark items across weeks and send you an alert when one of those items is on sale.

Android https://play.google.com/store/apps/details?id=com.codylab.halfprice

iPhone https://apps.apple.com/au/app/half-price-grocery-deals/id1453645622