Package manager for Busybox

Is there a package manager for busybox devices? After all, Busybox utilities are quite restricted. I suppose one would have to compile it for specific device. Suppose that you have a device running a Linux kernel and using a Busybox binary for all tools and such. Now suppose that you want to install some software on the device. Busybox doesn't have a package manager integrated, unless you count rpm as one. So you have to install that first. How would you do it? The OS in question is Linux.