Instaling app without AppStore, Jailbreak or any warranty void itp.?
A person can deploy apps to their own iOS devices using Xcode without a developer account, and without breaking/modifying the OS.  All one needs is an Apple ID, and a Mac running a recent version of Xcode (7.3.1 or later).  This is an Apple approved method of installing apps (designed for educational purposes).  Xcode will generate the needed personal provisioning profiles automatically.  

You can search for instructions online (here are a few examples: Xcode 7 develop for iOS without developer account and http://blog.ionicframework.com/deploying-to-a-device-without-an-apple-developer-account/ )

Apps installed using personal provisioning will be time limited (expire in somewhere around one week to one month).