Both GRAC and GRAAL are written with AMOS, by the same author.
They're point 'n click adventure (ala Monkey Island/Simon The Sorceror/etc) game makers. Given the fact they're written in AMOS they seem pretty decent.
Both are available on aminet, as is the source code (not needed if a person wants to make a game with them, but potentially handy nonetheless).
There's also some user newsletters and extras for both.
Additionally you can find some games made with them on aminet (I'm not sure, but I think H.O.L. will have a filter, or at least some adventure games made with them will detail the fact).
Other than a basic general knowledge of them, having read about them in magazines, etc. I don't know much more.
