Is Zork 1-4 free in north America to use and re-distribute if you don't charge? For example, can I print it and give it to people without it be under some kind of copyright rules?
I doubt it.
Honestly, I wondered if I should even post those links here.
The author (Meretzky) has publicly stated that he thinks we should be able to download all his old stuff (emphasis on the old) for free. The company he worked for, who actually owns the stuff, has publicly stated that he does not own the rights, though.
Someone not charging for it doesn't really make any difference.
If they (meaning the company who owns the rights) could possibly make money by selling it, and someone is sharing it online for free, the company who owns it is technically losing money with every download (or view).
Even if something is out of print, like that first book appears to be:
... they can still sue for someone stealing possible sales.
It happened with Nintendo and all the abandon-ware sites not too long ago. You could get every single NES ROM from those sites, until Nintendo was made aware of it. They made everyone take all that stuff down. Then, they released the NES mini and the SNES mini to un-abandon-ware everything, just to be sure.
In the end, everything I've read where people are asking about copyright and the limitations of fan-fiction or mods or "educational purposes" or any of that, it all ends up saying it's a gray area -- like an "ask for forgiveness, not permission" type of thing.
My advice (or thoughts or whatever)? Using other people's intellectual property without their consent is stealing. If you wrote a short story with an original character then saw that someone else was using your character in something and their thing was popular mainly because everyone liked your original character, you'd probably feel like someone wronged you -- depending on how much you need (or like) money -- or how you feel about the way your character is being used. And that's just one character we're talking about, not an entire world you created.
I'm at least half full of crap, though, because I only care what the actual creator says, not his corporate masters.
Like, George Lucas always applauded Star Wars fan-fiction. He loved that people loved Star Wars.
Stephen King, on the other hand, doesn't want anyone even referring to the Dark Tower without getting Sony's permission first.
Also, now that Lucas is "retired", the mouse will sue you if you post Star Wars fan-fiction.
So, there's no telling what might happen, now or in the future, if you include other people's stuff in your work. The Man might show up one day and say you can't share your work anymore because of it. (Just look at old TV shows on DVD. We can't even get the last of the old Muppet Show because they can't secure the rights on all the music in the live performances and such. And Beavis & Butt-head excludes the parts with them watching the dumb music videos.)
That's why Disney is so slick. They only use stuff from the public domain (mostly).
Anyway, unless I had it in writing that I could use someone else's IP in something I planned to publish, I would not include anything that wasn't created solely by me.
And that is why I'm poor. :)
I don't think anything could stop you from using the same structure and just changing the story elements and characters, though.
Like, I could probably emulate this series, calling it A WTF-Do-I-Do-Now Story © ™ ®.
I mean, he stole the Choose Your Own Adventure style, and I never heard about him getting in trouble.