Check out the Adventure Game Studio website for freeware games. Created by amateurs using the AGS engine made by Chris Jones (whom you may know as Tex Murphy) some are surprisingly good and one or two are, IMO, as good as pro games if, perhaps, not as polished. Here's their listing of
Award Winners.
I'm not sure you'll find anything like Myst, but it's worth a look.
Gil.
Btw, I do believe Ascovel has at least one game in that list of award winners.