DOS 3.3 & ProDOS & other Apple II OSs

[Gabriel Morales <Togega@Concentric.net>]

I am writing a small piece for new Apple II users. Since I only use a
few applications on my Apple II, I have a few questions:

What are the fundamental differences between DOS 3.3 & ProDOS to a new
Apple II user?

For which is there more software available?

What other operating systems are available for the Apple II (I know of
at least the GS OS, of course)?

On what models do these run?