Hm, alternativeto says that grayjay is proprietary

But it doesn’t seem to have it’s source publicly available

By in-game manual I meant a manual which built directly into the game and a main character could read it, not just a player who opened a PDF outside the game. And also usually those manuals are stylized, like in papers please (which I forgot to mention in the post btw) or like in Uncle Chop’s rocket shop

I already know about this game, and I even mentioned it in the post

Okay thanks