Installer 4.0 is now available in Cydia and is compatible with iOS 4.3.x firmware and below. Installer was the first jailbreak app store, back before Apple even announced the official App Store, but disappeared when RipDev stopped developing it. Cydia quickly came along to fill the gap, but now the Infini-Dev team has brought it back.
Yesterday we had success "porting" Installer to 4.3.3 and below. Installer works with a different system than Cydia, thats why you won’t be able to add a Cydia repo into installer. As we speak we are working on a new community source for installer only, which means you will be able to install things via installer.
We could use help, you may help us by submitting apps that where hosted by installer, or apps that have the installer structure. Or by making apps with a installer structure.
To get Installer on your iPhone just add http://fr0stdev.co.cc/repo to your repo list in Cydia. The apps available are few and far between right now, so using Installer isn't going to be a great experience until more contributions are made and a new community source is up and running.
When we tested Installer we ran into a MobileSubstrate issue so we had to run it in Safe Mode, and the landing page also presented us with a 403 error. So it looks like they've got a few bugs to hammer out. Still, it's nice to have options. Let us know if it's working any better for you in the comments!