Smartprix - Smartprix is an app by Smartpix.
AliPrice - AliExpress Price Tracker app lets you track the price history of any item from many online retailers like AliExpress, Daraz, and Amazon, etc.
idealo - Idealo is a free to use mobile application that helps you to find products, compare price and make an informed decision.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Tripadvisor - The Tripadvisor mobile app is available for the Android and iOS platforms. It can be used to create reviews of hotels, restaurants, and to chat with other travelers on Tripadvisor forums.