Checkra1n is basically a jailbreak tool that allows users to gain access to the root file system of Apple devices, such as iPhones and iPads. This allows users to install custom apps, themes, and extensions that are not available on the official App Store. The jailbreak is based on a bootrom exploit that affects devices with A5-A15 chips, meaning that it can be used to jailbreak devices from the iPhone 4s to the iPhone 14. The tool is available for Mac, Linux and Windows platforms and was developed by a team of hackers and security researchers. In addition to jailbreaking, Checkra1n also allows users to bypass iCloud activation locks on iPhones, enabling them to access the device and its features even if it is locked to another user's iCloud account.