Pegasos II 750GX CPU card.
Pegasos II 7447A CPU card.
Pegasos II 7448 CPU card.
AFAIK they all were prototyped and fully working, and serves as good examples of hardware that exists but never managed all the way to the market due to other reasons than technical.
I think the most common reasons for most of the hardware on this list ending up as vapor, is because of the huge obstacles that *follows* design and prototyping; that is setting up actual production which requires monumental efforts in arranging component supplies, financial strength (a long haul required). Obviously, designing hardware is nothing. Actual prototyping requires a little more (most HW on your list are designs only, many was never prototyped AFAIK), but when it comes to actual end-user production - here is where most projects gets abandoned!
When you have everything prototyped and tested, you ask yourself: "OK now, is this really worth the risk? When will I get the enormous big sum of invested money back, if *ever*? Is there really a market? Will the turnover be high enough or should I focus on something else?"
