Cydia is similar to installer, in that it’s a package management system for the iPhone/iPod Touch, written by Jay Freeman (Saurik), but in reality it’s a whole lot more than that; Cydia is a graphic user interface for APT on the iPhone/Touch.

APT or ‘Advanced Packaging Tool,’ is the main package distribution system for Linux systems, and has been ported to many others including UNIX, Mac OS X (available in Fink), and now the iPhoneOS! There are many APT front-ends for Linux and other systems including ‘aptitude,’ and ‘Synaptic Package Manager.’ This is basically what Cydia is to the iPhone. (This also means that you can apt-get any of the cydia packges from a terminal window or ssh, right *on* the phone)

Jay Freeman (Saurik) writes on his website:

“In general, Cydia works very similarly to Installer, allowing people to quickly get up and running with the newer software. The main interface component is a bar of buttons along the bottom that provide access to the different main screens of the application.”

For the most part, Cydia is just like installer in terms of user interface, with a few exceptions. The ‘Updates’ tab has been renamed to ‘Changes,’ where all of the packages updates *and* new packages are listed. Updates are located at the top whereas new packages are listed below, in reverse chronilogical order; this replaces the ‘Recent Packages’ category in Installer. The second main differance is the ‘Uninstall’ Tab has been renamed to ‘Manage,’ which is actually much better fitting. Not only can you browse and uninstall all of the applications and utilites that you currently have installed, but you also have the option to reinstall them, all from one screen. This means no more uninstalling from one tab, and having to go back any find the applications you wish to install again from another.

The final difference between Installer.app and Cydia is the sources editor. You may notice that in Cydia, well, there isn’t one. Truth is it’s being still being worked on, but had to be placed on the backburner due to all of the 2.0 and Pwnage drama that arrised in the last software update. The goal is for the sources editor to be placed in Settings.app, instead of having it clutter up Cydia itself, and is now a priority and should be finished soon.

For more information about Cydia and APT on iPhoneOS, we encourage you to take a gander at this post on Saurik’s website which goes into much greater detail about what Cydia is and its full potential.