UK resellers wanted to be first to new deals on Facebook Marketplace, eBay, Gumtree and other sites. We built Marketplace Monitor with a Python back end and a FlutterFlow app: it watches each user's search terms across marketplaces in real time and sends a push alert the moment a new listing appears. It's live on the App Store and Google Play, active since June 2024, with 4 subscription tiers and 6 languages.