Icy was a lightweight APT package installer that was both themeable and produced in over 30 languages. It worked perfectly on iPhoneOS 2.x-3.1.2, and it was updated for iOS 4 by many. Icy was a very advanced installer but it had its issues. RiPDev tried to reinvent APT, losing a lot of popular features and made the repository maintainers have to do a lot more work than they would have for Cydia. Saurik explained this when Icy was released some time back. Since RiPDev closed their business, they made Icy open source.
The WeAmDev team picked up the Icy project, releasing the 2.0.1 version featuring iOS 4 multitasking support and the improved Icy 2.1. As of now, Icy is being developed by Infini-Dev, but it has been stated on Twitter that Icy has been returned to WeAmDev.