For PageMaker, you probably need open them in PM 6, 6.5, or 7.0 to do anything useful, those are the ones that offer cross-compatibility with InDesign (I think they have an save as .indd option, if not InDesign should open the PM native file). If you are desperate I may have an old PM 6.5 disk lying around. Whether it'll install on modern hardware is another matter (and I can't remember if it worked without registration). Never tried Scribus (well, I did once, never got past the installation instructions).
No idea about WriteNow, it's truly ancient. You might be able to simply rename as .txt and pull the text out of it – depends on whether it's RTFy or a binary format, if it's the latter you're probably stuffed.
If Windows doesn't recognise the disk, it's probably Mac formatted. Or the dye has degraded and you have, in your hands, a piece of pointless plastic.