KnossOS is a free text-based psychological horror game. It involves a Unix-like operating system, retro modem sound effects, and blurring of lines between player and character. It is *not* a visual novel as I have had to class it as, but that seemed the closest genre.
Admittedly, screenshots of the game don't look especially impressive. This is due to the facts that the game is text-based, so there aren't really any graphics, and that I wanted to avoid spoilers.