This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
ProDOS has lots of nice features-- mainly, you can create sub- directories, diskettes ("volumes") can be named, and ProDOS works well on hard disks. The GS System 6 Finder can handle ProDOS files and launch programs from ProDOS diskettes. ProDOS's BASIC command interpreter shares many commands with DOS 3.3, too; so, it is not difficult for DOS 3.3 users to get started with the newer operating system. By: David Empson