Oh Installer, Installer, we had so much fun together, you and I. When Apple didn't have any iPhone app store, and whenever Apple blocked some essential iPhone apps, you were always there. And now... now you are dead.
The short story is that Cydia—the other non-official iPhone app installer—won the battle against Installer. Installer was the first pretty application installer to appear for the iPhone, but Cydia became more popular over the last few months. Ripdev—which was involved in the project since version 3—says that the Installer repositories will be available until July 1st, 2009.
But fear not, my young apprentices, because we still have Cydia and Icy, which is an iPhone app installer that plugs into Cydia directories—incidentally, made by the same guys who did Installer. [Ripdev]