I learned that Pine allows you to setup labels/tags just like Gmail! Pine calls labels/tags "keywords." Pine is available as a stand-alone email client on virtually every operating system including Unix, Linux, Mac OS X and Windows. I've always enjoyed using Pine, but now I like it even more!
Incidentally, I also learn that the next version of Pine will be called Alpine (the name has been changed because Alpine uses an open-source type license whereas Pine uses a restricted license).