Fallout Pip-Boy is a free-to-play Fallout 4 companion app for Windows Phone, iOS, and Android devices that was announced at Bethesda's E3 2015 press conference on June 14, 2015. The app was released on November 4, 2015. It allows Fallout 4 players to access the functions of their Pip-Boy 3000 Mark IV remotely to manage inventory, check stats and perks, peruse the map, and even play acquired minigames.
The app functions almost identically to the in-game Fallout 4 Pip-Boy, minus the ability to zoom with the map and other small features. A game option in Fallout 4 allows you to sync the in-game Pip-Boy with the app, thus enabling you to see your acquired items and completed quests like you would be seeing them in the game.