Okay, first of all, there aren't any trainers or hex editors for Myst. You don't even have a character in Myst, much less any stats, skills, hit points,
or even an inventory you might conceivably want to edit. I don't really have any idea what people who ask me for a "Myst character editor" are really even
looking for. The only way to really cheat in this game is to look up the solution to a puzzle rather than figuring it out yourself. You can actually win the game
without ever leaving Myst Island this way, if you already know the code that will lead you to Atrus and the way to reveal the last linking page. (Some people
call this a glitch, but as far as I'm concerned it would be ridiculous for it to be any other way--of course, if you were psychic and knew the codes already,
you wouldn't have to bother with the adventure. It's not like passwords only function if you've found them legitimately in the real world!)
Anyway, so there's not much cheat to be had on Myst, but if you need a puzzle solution or just want to learn more about this classic game, here are a few
good links for you:
My Myst Pages:
Myst Hints, with general gameplay information and suggestions.
Myst Walkthrough, with possible optional actions in each game location (low-spoiler).
Myst Review, with a spoiler-free overview of the game for those considering playing.
Universal Hints System is a great place to get a spoiler for one specific puzzle you're stuck on without accidentally ruining any of the rest of the game--they have
their walkthrough uniquely structured to reveal only one hint at a time.
Here is the official Myst homepage from Cyan Worlds. You can get Myst art, music, screenshots, and a patch for older versions of the game here.
Here's the Myst Masterpiece page from UbiSoft, who picked the series up after Riven and released the digitally remastered version of Myst. Tech support and press releases.
Myst Obsession is the most thorough, useful Myst resource I've found online, with screenshots, wallpaper and fan art, and a forum.
Myst Community is another good Myst forum, with separate sections for each game and for certain Myst-related topics.
The rest of these links aren't related to Myst, but you may enjoy them anyway... most of them were created by me or by friends of mine. (-: