On IOS 4 and 5
In May 2011, a team of developers called Infini-Dev recreated Installer 4 so that it could be run on iOS 4 and above, although the main current repositories are only compatible with Cydia and no longer compatible with Installer. RiPDev has put their old Installer repo back online since Infini-Dev released Installer, and there are also some other repos like Greek-iPhone who offer up to date packages for Installer.
Read more about this topic: Installer.app