I would like to use a package manager to generate a list of all installed packages that are not depended on by any other installed package.

That is to say, a list of installed packages that are not required by any other installed package.

I believe these are referred to as packages with 0 forward dependencies. I believe they are also called "leaves."

I am on Red Hat, so a method of doing this with rpm, yum or smart would be optimal.

I discovered the package-cleanup program that is a part of yum-utils. According to package-cleanup's man page, the option --leaves will "list leaf nodes in the local RPM database. Leaf nodes are RPMs that are not relied upon by any other RPM." I thought this would do what I wanted, but it seems to do a poor job. It listed only two packages. While those two packages are indeed required by nothing else, I am sure there are many more than two on my system. (For example, it did not list firefox)

Excuse me. I discovered the source of my trouble mere seconds after posting.

I was using this command: package-cleanup --leaves

However, by default, that only shows library leaves. This is what I wanted:
package-cleanup --leaves --all