Dreamweb is a fascinating (non-IF) game. If you already know about it, and the friction between what the feelie tells you and the actual game’s reality, you don’t need to expand this box. If you do, go ahead. Some spoilers, but no puzzle spoilers or anything. Nothing that the game isn’t up front about.
In Dreamweb, you are assigned by entities to save the world by eliminating impostors; aliens (or something, I don’t remember 100%) which are impersonating humans (like pod people) and are working to be the downfall of the human race. Your heroic task is to kill them.
However, the feelie that accompanies the game makes you seriously question the PC’s sanity. And you will soon realise that he may not be doing what he thinks he’s doing.
What I love about it is that the game itself sticks to its reality doggedly. Never lets up. There is never a nod, a wink, towards the player that helps resolve this definitively one way or the other. Within the game, it’s as though we are within the PC’s mind, and his perception is what we get. His verison of events. The game sticks to it and never, ever gives you any reason to doubt the premise or his actions.
And the feelie is very much a part of the game, but it’s an external part. It’s not coded in the game. The feelie will sow doubts on you. Doubts that you will not get by simply playing the game. This is a game that truly exists completely only with its feelie, not for atmosphere or copy-protection but truly as part and parcel of the story, giving the game a dimension that the game, by itself, doesn’t have - because the game, by design, is sticking doggedly to only one version of events.
I find this fascinating.
Any other games that have attempted this? And there are many “thises” in play, so I’d like to focus on a game that focuses on presenting, unrelentingly, a reality to the player, and doesn’t let up, and doesn’t give any clues about the veracity of that reality… and complements that with an external twist (one that comes with the game, preferably offline) that calls the game’s reality into question, completely externally.
There are a significant number of games which play havoc with your perception, and I love them, but usually the key to unveil the reality - or the various realities - is, at some point, in the game itself. The game might be very very very tight-fisted with its clues, making them potentially more powerful when they land, but they are usually there.
Is there any other game that has tried something like this? Have the game doggedly stick to a reality, unrelentingly… and question that reality through a feelie? Not even an AMUSING section; not even its help menu; not even the game giving you a password to open a RAR file upon completion; nothing. A game that, as far as you know, is exactly what it is. But when vieweing the feelie, it upends the whole thing on its head.
I seem to remember some Inform 7 games that were released along with their source code as part of a… competition? Jam? I think Ryan Veeder was involved?, but I could be mistaken…, and for some of them vieweing the source code separately was very much a part of the experience. That comes close, but I don’t remember one of those games actually distorting the reality of the playable game by the existence of the source code; instead, I remember them enhancing the experience.
Thoughts? 
Regardless, it was a gutsy thing for Dreamweb to do. Apart from that, the game itself is fun but not really remarkable. But this layer of uncertainty, and the game’s insistence in absolutely not breaking character, is quite an experience.