LogInA perfect toolkit for horror games and puzzles.
Check out a demo of a NonEuclidean rendering engine for Windows, written in C++ OpenGL that allows creating all kinds of illusions.
How does it work? It is just like the Portal games, but there are no portal seams and there are more than two of them. The developer pointed out that there are several surfaces that are actually solid geometry with textures on top of them. When you walk through this texture, the engine teleports you to another area and you get this strange illusion.
Sound pretty easy, right? Actually, it's a bit challenging to render. Each surface has to recursively render surfaces behind it conditionally depending on if it's occluded or not from each perspective," noted the developer. He couldn't do it with Unity, so he decided to write his own engine in OpenGL. This toolkit could be used for adventures, puzzles, and all kinds of crazy horror games.
Make sure to check out the engine page on GitHub.