The apps listed here are publicly known to be built with Xamarin.Forms.
For a lengthy list of customer case studies and endorsements, visit the Xamarin Customer page.
https://play.google.com/store/apps/details?id=br.com.JetEbusiness.ZapCommerce
https://itunes.apple.com/us/app/hospitality-by-gladtohaveyou/id1281580838?mt=8
https://play.google.com/store/apps/details?id=com.gladtohaveyou.hospitality&hl=en_US
https://blog.xamarin.com/how-olo-powers-150-restaurant-loyalty-apps-with-mobile-devops/
https://itunes.apple.com/us/app/guess-jeans/id687484959?mt=8
https://play.google.com/store/apps/details?id=com.alert.guess&hl=en
https://itunes.apple.com/us/app/mile-of-music/id900485335?mt=8
https://play.google.com/store/apps/details?id=com.skylinetechnologies.mileofmusicnew&hl=en
https://itunes.apple.com/us/app/imsa/id789830071?mt=8
https://play.google.com/store/apps/details?id=com.imsa.app&hl=en
https://itunes.apple.com/us/app/zurich-airport-app/id484076423?mt=8
https://play.google.com/store/apps/details?id=ch.zurichairport.flughafenapp&hl=en
https://itunes.apple.com/us/app/freshdirect/id346631494?mt=8
https://itunes.apple.com/us/app/foodkick/id1049036650?mt=8
https://blog.xamarin.com/mobile-devops-at-coca-cola-bottling-co-consolidated/
https://blog.xamarin.com/minnesota-twins-hits-home-run-cloud-powered-scouting-apps/
http://motzcod.es/post/155442565087/scoreboard-keep-track-of-game-scores-app
https://itunes.apple.com/us/app/pool-math-by-troublefreepool/id1228819359?mt=8
https://play.google.com/store/apps/details?id=com.troublefreepool.poolmath&hl=en
https://blog.xamarin.com/guitar-centers-five-star-xamarin-forms-apps-bring-music-masses/
https://itunes.apple.com/us/app/nintendo-switch-online/id1234806557
https://play.google.com/store/apps/details?id=com.nintendo.znca&hl=en
https://itunes.apple.com/us/app/highrise-small-business-crm/id964271435?mt=8
https://play.google.com/store/apps/details?id=com.highrisehq.android
https://itunes.apple.com/us/app/savedapp/id1320664236?l=nb&ls=1&mt=8
https://play.google.com/store/apps/details?id=net.johansen.savedioapp
Pockit in the UK is built in Xamarin Forms, I worked on it.