App Vault is an app developed by Xiaomi Inc. that provides a collection of app cards that make it easy for users to open apps, access data, and read the latest news. It is easily accessed by swiping the home screen to the right. App Vault is designed with user privacy in mind and only collects the user data necessary to provide services. It is available in all markets and compatible with MIUI versions 11, 12, and 12.5.

In addition to the above, there is also an app called "Vault - Hide photos & videos" available on the App Store. This app is designed to protect and hide private photos and videos, and it can back up all your photos and videos on Cloud. It also offers space encryption, bulk photos and videos import, and intelligent folder management to keep your phone organized.

It is important to note that there is a Reddit thread discussing the purpose of App Vault, with some users suggesting that it has some functionality with Xiaomi account. However, it is not clear what this functionality is.