Cydia

Cydia is a graphical user interface of APT for iOS. It enables a user to find and install software unauthorized by Apple on jailbroken iPhones, iPads and iPod Touch devices. It also refers to the digital distribution platform for software on iOS accessed through Cydia software. Most of the software packages available through Cydia are free of charge, although some require purchasing.

Cydia is developed by Jay Freeman (named "saurik") and his company, SaurikIT. The name "Cydia" is a reference to the moth genus Cydia, notably the codling moth (Cydia pomonella), which eats fruits such as apples and pears.

Cydia provides a graphical user interface (GUI) to jailbroken devices using Advanced Packaging Tool (a package manager) repositories to install software unavailable on the App Store. Cydia is based on UIKit and was written by Jay Freeman after porting APT to iOS as part of his Telesphoreo project.

Packages are downloaded through the list of repositories a user has installed. Apps are installed in the same location as Apple's own applications, in the /Applications directory. Jailbroken devices can also still buy and download apps normally from the official App Store. Some jailbreaking tools install Cydia automatically, while others may not.

Some of the packages available through Cydia are standard applications, while most packages are extensions and modifications for the iOS interface and for apps in the iOS ecosystem. Some Cydia repositories host open source packages as well as paid modifications for jailbroken devices. These modifications are based on a framework called Cydia Substrate (formally MobileSubstrate).

Many ports of existing POSIX-compliant command line tools are available on Cydia as well, including bash, coreutils and OpenSSH, meaning the device could potentially be used as a full-fledged BSD workstation, although missing some development tools.

In March 2009, the now-defunct blog TUAW (The Unofficial Apple Weblog) announced that the Cydia Store, the in-app software purchasing system for Cydia, had opened for sales. The announcement also mentioned that Amazon payments was the only option available, but that PayPal would be added in the future. PayPal later became a payment option as well. Cydia stopped accepting Amazon Payments in 2015, leaving PayPal as the sole payment option. After a bug related to PayPal's digital token authorization was discovered via TechCrunch, Freeman decided to shut down the Cydia Store on December 16, 2018.

The risks in jailbreaking are mixed. Advocates offer that developer tools installed from Cydia can help add extra security. However, being able to install untrusted third-party software can cause data loss and malware. Cydia Substrate, the code injection library usually installed alongside Cydia, will detect if an installed package causes SpringBoard to crash, and will reboot it in a "safe mode", with all third-party packages temporarily disabled.